core: MoveOrCopyDiskCommand - reduce query count

When loading the vms for a disk, the vm device information is already
loaded - therefore there's no need to filter it out and then reload it
for each vm, we can use the values that were loaded during the first
query execution.

Change-Id: Ic4b15114bc72dc07de917692b60703008008ae13
Related-To: https://bugzilla.redhat.com/show_bug.cgi?id=1032807
Signed-off-by: Liron Aravot <laravot@redhat.com>