Description of problem:
Via SDK, Download disk image & try to pause it at 50% download, the download stop & rollback - I would expect it to continue the download.

Also, the download although only 50% was done, by Event log it finishes successfully, see "Finalizing successful transfer" at engine log.
I would expect to see an error about this invalid pause attempt.

2018-05-29 16:09:03,488+03 ERROR [org.ovirt.engine.core.bll.storage.disk.image.TransferImageStatusCommand] (default task-17) [a029e7cd-ef3f-449f-a1c8-c6670e3aeb6c] Invalid parameters: cannot move an image downlo
ad to any kind of a paused state as the download is handled by the client and cannot be paused. Note that a download can be canceled if you wish to stop it.
2018-05-29 16:09:03,496+03 ERROR [org.ovirt.engine.core.bll.storage.disk.image.TransferImageStatusCommand] (default task-17) [a029e7cd-ef3f-449f-a1c8-c6670e3aeb6c] Transaction rolled-back for command 'org.ovirt.
engine.core.bll.storage.disk.image.TransferImageStatusCommand'.
2018-05-29 16:09:03,498+03 ERROR [org.ovirt.engine.api.restapi.resource.AbstractBackendResource] (default task-17) [] Operation Failed: []
2018-05-29 16:09:03,619+03 INFO  [org.ovirt.engine.core.bll.storage.disk.image.TransferImageStatusCommand] (default task-6) [3f55968e-3ed2-410e-a8b1-b68509b43184] Running command: TransferImageStatusCommand inte
rnal: false. Entities affected :  ID: aaa00000-0000-0000-0000-123456789aaa Type: SystemAction group CREATE_DISK with role type USER
2018-05-29 16:09:03,622+03 INFO  [org.ovirt.engine.core.bll.storage.disk.image.ImageTransferUpdater] (default task-6) [3f55968e-3ed2-410e-a8b1-b68509b43184] Updating image transfer be4cd43b-1a21-4276-8e16-65fdc8
d182fa (image 927cb30d-d38d-4660-8f71-7dd7361eb62c) phase to Finalizing Success
2018-05-29 16:09:05,741+03 INFO  [org.ovirt.engine.core.bll.storage.disk.image.TransferDiskImageCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-81) [06bfb499-133d-4ea5-9f94-a69a63594f9e] Finalizing succ
essful transfer for Download disk 'disk_virtiocow_2916030102' (disk id: '927cb30d-d38d-4660-8f71-7dd7361eb62c', image id: '34bccad2-86ee-4468-b2ad-351287af95f3')
2018-05-29 16:09:05,744+03 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.RemoveImageTicketVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-81) [06bfb499-133d-4ea5-9f94-a69a63594f9e] START, RemoveIm
ageTicketVDSCommand(HostName = host_mixed_1, RemoveImageTicketVDSCommandParameters:{hostId='a354bdbb-953b-4ce3-9e0a-66672b5b33cb', ticketId='a12f6bc3-b600-492c-aa72-aa20776c38ff', timeout='null'}), log id: 3d870
0d7
2018-05-29 16:09:05,766+03 INFO  [org.ovirt.engine.core.vdsbroker.vdsbroker.RemoveImageTicketVDSCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-81) [06bfb499-133d-4ea5-9f94-a69a63594f9e] FINISH, RemoveI
mageTicketVDSCommand, return: StatusOnlyReturn [status=Status [code=0, message=Done]], log id: 3d8700d7
2018-05-29 16:09:05,766+03 INFO  [org.ovirt.engine.core.bll.storage.disk.image.TransferDiskImageCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-81) [06bfb499-133d-4ea5-9f94-a69a63594f9e] Successfully st
opped image transfer session for ticket 'a12f6bc3-b600-492c-aa72-aa20776c38ff'
2018-05-29 16:09:05,766+03 INFO  [org.ovirt.engine.core.bll.storage.disk.image.TransferDiskImageCommand] (EE-ManagedThreadFactory-engineScheduled-Thread-81) [06bfb499-133d-4ea5-9f94-a69a63594f9e] Removing image 
ticket from ovirt-imageio-proxy, id a12f6bc3-b600-492c-aa72-aa20776c38ff
2018-05-29 16:09:05,793+03 INFO  [org.ovirt.engine.core.bll.storage.disk.image.ImageTransferUpdater] (EE-ManagedThreadFactory-engineScheduled-Thread-81) [06bfb499-133d-4ea5-9f94-a69a63594f9e] Updating image tran
sfer be4cd43b-1a21-4276-8e16-65fdc8d182fa (image 927cb30d-d38d-4660-8f71-7dd7361eb62c) phase to Finished Success

Version-Release number of selected component (if applicable):
4.2.4-0.1.el7

How reproducible:
100%

Steps to Reproduce:
Via SDK only :
1.Start disk image download
2.When it reaches about ~50% download pause transfer

Actual results:
Download stop & rollback but in event log it states it finished download successfully.

Expected results:
1) The download should not stop.
2) If the download stops from an invalid action(pause) it should be stated in engine event log that it was finished successfully.

Additional info: