restapi: adding support for moving a VM disk

* Added move action to VmDiskResource interface.
* Added the implementation in BackendVmDiskResource.
* Added tests to BackendVmDiskResourceTest (similar to the tests
  of copy disk in BackendTemplateDiskResourceTest).
* Updated rsdl yaml accordingly (similar to copy disk).
* Deprecated move VM (replaced by move disk)
  I.e.
  deprecated '/api/vms/{vm:id}/move|rel=move'
  replaced by '/api/vms/{vm:id}/disks/{disk:id}/move|rel=move'

Change-Id: I1c864a81463388f8ac82eba6f909c5a4359efab6
Bug-Url: https://bugzilla.redhat.com/883871
Signed-off-by: Daniel Erez <derez@redhat.com>