core: update VirtIO-SCSI device on next run VM snapshot

* Added an 'EditableDeviceOnVmStatusField' annotation for
  'virtioScsiEnabled' (in VmManagementParametersBase).
* Consequently, removed canDo validation in UpdateVmCommand.

Change-Id: Ic1ee50f25e71d4540ebb6ab60250b9cfa5985ac4
Bug-Url: https://bugzilla.redhat.com/1035289
Signed-off-by: Daniel Erez <derez@redhat.com>