Description of problem:
Taking a snapshot on gluster fails 

Version-Release number of selected component (if applicable):
ovirt-engine-4.2.2.1-0.1.el7.noarch
vdsm-4.20.19-1.el7ev.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Create a VM with:
- 1 bootable disk (doesn't matter type).
- 1 preallocated disk on gluster SD (5 GB in my case).
2. Start the VM.
3. Under Compute -> Virtual Machines, select the newly created VM and click on name.
4. Switch to Snapshot tab.
5. Click on 'Create' and in the dialog window:
- Give the snapshot a descripiton.
- select the second disk (gluster)
- uncheck the 'Save Memory'.
6. click 'OK'

Actual results:
The Snapshot is been created.
The actual size of the disk is been appended by the size of the Virtual size.
The Allocation type changes to thin provision.

Expected results:
The Snapshot is been created.
The actual size of the disk is the same as the Virtual size.
The Allocation type stays preallocated.

Additional info:
Error from engine log:
2018-02-28 16:18:40,392+02 INFO  [org.ovirt.engine.core.bll.ConcurrentChildCommandsExecutionCallback] (EE-ManagedThreadFactory-engineScheduled-Thread-6) [a17e4adb-3f23-4852-a62b-15e164efdffc] Command 'CreateAllSnapshotsFromVm' id: 'e767d659-c360-4ffb-ad76-1f9ca7066f4a' child commands '[5aff62a3-02ef-4d57-bc71-ccca71b56175]' executions were completed, status 'SUCCEEDED'
2018-02-28 16:18:41,443+02 INFO  [org.ovirt.engine.core.bll.snapshots.CreateAllSnapshotsFromVmCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] Ending command 'org.ovirt.engine.core.bll.snapshots.CreateAllSnapshotsFromVmCommand' successfully.
2018-02-28 16:18:41,462+02 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.SnapshotVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] START, SnapshotVDSCommand(HostName = new_Host_13, SnapshotVDSCommandParameters:{hostId='c361762d-115c-4850-a1de-ae6cbe5d3561', vmId='b8e5be38-b5af-4e92-9d0d-16a70c888440'}), log id: 4abe668f
2018-02-28 16:18:41,468+02 ERROR [org.ovirt.engine.core.vdsbroker.vdsbroker.SnapshotVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] Failed in 'SnapshotVDS' method
2018-02-28 16:18:41,480+02 ERROR [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] EVENT_ID: VDS_BROKER_COMMAND_FAILURE(10,802), VDSM new_Host_13 command SnapshotVDS failed: Snapshot failed
2018-02-28 16:18:41,480+02 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.SnapshotVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] Command 'org.ovirt.engine.core.vdsbroker.vdsbroker.SnapshotVDSCommand' return value 'StatusOnlyReturn [status=Status [code=48, message=Snapshot failed]]'
2018-02-28 16:18:41,480+02 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.SnapshotVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] HostName = new_Host_13
2018-02-28 16:18:41,481+02 ERROR [org.ovirt.engine.core.vdsbroker.vdsbroker.SnapshotVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] Command 'SnapshotVDSCommand(HostName = new_Host_13, SnapshotVDSCommandParameters:{hostId='c361762d-115c-4850-a1de-ae6cbe5d3561', vmId='b8e5be38-b5af-4e92-9d0d-16a70c888440'})' execution failed: VDSGenericException: VDSErrorException: Failed to SnapshotVDS, error = Snapshot failed, code = 48
2018-02-28 16:18:41,481+02 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.SnapshotVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] FINISH, SnapshotVDSCommand, log id: 4abe668f
2018-02-28 16:18:41,481+02 WARN  [org.ovirt.engine.core.bll.snapshots.CreateAllSnapshotsFromVmCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] Could not perform live snapshot due to error, VM will still be configured to the new created snapshot: EngineException: org.ovirt.engine.core.vdsbroker.vdsbroker.VDSErrorException: VDSGenericException: VDSErrorException: Failed to SnapshotVDS, error = Snapshot failed, code = 48 (Failed with error SNAPSHOT_FAILED and code 48)
2018-02-28 16:18:41,510+02 WARN  [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] EVENT_ID: USER_CREATE_LIVE_SNAPSHOT_FINISHED_FAILURE(170), Failed to create live snapshot 'aaa' for VM 'test_VM'. VM restart is recommended. Note that using the created snapshot might cause data inconsistency.
2018-02-28 16:18:41,530+02 INFO  [org.ovirt.engine.core.bll.snapshots.CreateSnapshotCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] Ending command 'org.ovirt.engine.core.bll.snapshots.CreateSnapshotCommand' successfully.
2018-02-28 16:18:41,550+02 INFO  [org.ovirt.engine.core.vdsbroker.irsbroker.GetImageInfoVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] START, GetImageInfoVDSCommand( GetImageInfoVDSCommandParameters:{storagePoolId='5d567ca7-069a-490c-9800-09ac6fd3a781', ignoreFailoverLimit='false', storageDomainId='52838d3c-11d1-4a21-98f7-dfc4f8271583', imageGroupId='25ba3048-1114-4461-97e5-0d3a571b61a6', imageId='16fca9e1-af93-4832-b764-23f16562d34e'}), log id: 54504a99
2018-02-28 16:18:41,558+02 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.GetVolumeInfoVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] START, GetVolumeInfoVDSCommand(HostName = new_Host_12, GetVolumeInfoVDSCommandParameters:{hostId='25f281cf-0dbf-42c8-98d9-a9154b0f242b', storagePoolId='5d567ca7-069a-490c-9800-09ac6fd3a781', storageDomainId='52838d3c-11d1-4a21-98f7-dfc4f8271583', imageGroupId='25ba3048-1114-4461-97e5-0d3a571b61a6', imageId='16fca9e1-af93-4832-b764-23f16562d34e'}), log id: 2ac6dfb8
2018-02-28 16:18:41,609+02 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.GetVolumeInfoVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] FINISH, GetVolumeInfoVDSCommand, return: org.ovirt.engine.core.common.businessentities.storage.DiskImage@27d0786d, log id: 2ac6dfb8
2018-02-28 16:18:41,609+02 INFO  [org.ovirt.engine.core.vdsbroker.irsbroker.GetImageInfoVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] FINISH, GetImageInfoVDSCommand, return: org.ovirt.engine.core.common.businessentities.storage.DiskImage@27d0786d, log id: 54504a99
2018-02-28 16:18:41,630+02 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.GetQemuImageInfoVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] START, GetQemuImageInfoVDSCommand(HostName = new_Host_13, GetVolumeInfoVDSCommandParameters:{hostId='c361762d-115c-4850-a1de-ae6cbe5d3561', storagePoolId='5d567ca7-069a-490c-9800-09ac6fd3a781', storageDomainId='52838d3c-11d1-4a21-98f7-dfc4f8271583', imageGroupId='25ba3048-1114-4461-97e5-0d3a571b61a6', imageId='16fca9e1-af93-4832-b764-23f16562d34e'}), log id: 53b0f4d1
2018-02-28 16:18:42,211+02 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.GetQemuImageInfoVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [a17e4adb-3f23-4852-a62b-15e164efdffc] FINISH, GetQemuImageInfoVDSCommand, return: org.ovirt.engine.core.common.businessentities.storage.QemuImageInfo@552e5224, log id: 53b0f4d1
2018-02-28 16:18:42,241+02 INFO  [org.ovirt.engine.core.bll.snapshots.CreateAllSnapshotsFromVmCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [] Lock freed to object 'EngineLock:{exclusiveLocks='[b8e5be38-b5af-4e92-9d0d-16a70c888440=VM]', sharedLocks=''}'
2018-02-28 16:18:42,258+02 ERROR [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [] EVENT_ID: USER_CREATE_SNAPSHOT_FINISHED_FAILURE(69), Failed to complete snapshot 'aaa' creation for VM 'test_VM'.
2018-02-28 16:18:42,259+02 WARN  [org.ovirt.engine.core.bll.ConcurrentChildCommandsExecutionCallback] (EE-ManagedThreadFactory-engineScheduled-Thread-39) [] Command 'CreateAllSnapshotsFromVm' id: 'e767d659-c360-4ffb-ad76-1f9ca7066f4a' end method execution failed, as the command isn't marked for endAction() retries silently ignoring


Error from vdsm log:
2018-02-28 16:18:41,462+0200 INFO  (jsonrpc/6) [api.virt] START snapshot(snapDrives=[{'baseVolumeID': '62a8d8e9-d381-49b5-a200-d79c0c1e503d', 'domainID': '52838d3c-11d1-4a21-98f7-dfc4f8271583', 'volumeID': '16fca9e1-af93-4832-b764-23f16562d34e', 'imageID': '25ba3048-1114-4461-97e5-0d3a571b61a6'}], snapMemory=None, frozen=False) from=::ffff:10.35.163.132,56226, flow_id=a17e4adb-3f23-4852-a62b-15e164efdffc (api:46)
2018-02-28 16:18:41,463+0200 ERROR (jsonrpc/6) [virt.vm] (vmId='b8e5be38-b5af-4e92-9d0d-16a70c888440') The base volume doesn't exist: {'device': 'disk', 'domainID': '52838d3c-11d1-4a21-98f7-dfc4f8271583', 'volumeID': '62a8d8e9-d381-49b5-a200-d79c0c1e503d', 'imageID': '25ba3048-1114-4461-97e5-0d3a571b61a6'} (vm:4387)
2018-02-28 16:18:41,463+0200 INFO  (jsonrpc/6) [api.virt] FINISH snapshot return={'status': {'message': 'Snapshot failed', 'code': 48}} from=::ffff:10.35.163.132,56226, flow_id=a17e4adb-3f23-4852-a62b-15e164efdffc (api:52)
2018-02-28 16:18:41,463+0200 INFO  (jsonrpc/6) [jsonrpc.JsonRpcServer] RPC call VM.snapshot failed (error 48) in 0.00 seconds (__init__:573)