Description of problem:
Creating a VM from VM snapshot fails with error popup "User is not authorized to perform this action." if the user is not admin@userportal and has only role VmCreator.

Version-Release number of selected component (if applicable):
3.6.5, also tested on master (commit 6a84511)

How reproducible:
100%

Steps to Reproduce:
1. Create a VM
2. Create a snapshot of the VM
3. Pick a user and assign him system-wide role 'VmCreator', 'SuperUser' role for some unrelated VM (just to allow him to log in Webadmin) and make sure he has no other permissions.
4. Log to webadmin using user above.
5. Clone snapshot (step 2) to new VM
6. In "Clone VM from Snapshot" dialog set name only and press "OK".

Actual results:
Error dialog pops up: 
Operation canceled
Error while executing action:
<vm-name>:
    User is not authorized to perform this action.

Expected results:
VM is created.

Additional info:
It actually turned out that no user (even admin@internal) can adjust custom properties in "Clone VM from Snapshot" dialog.

Steps to reproduce:
(from Webadmin as admin@internal)
1. Create VM
2. Create a snapshot of the VM
3. Select "Clone" on the snapshot
4. Adjust Custom properties in "Clone VM from Snapshot" dialog
5. Confirm dialog wiht "OK"
6. Check custom properties of newly created VM in Edit VM dialog

Actual results:
no custom properties

Expected results:
Custom properties set in "Clone VM from Snapshot" dialog are reflected to the VM.