core: storage active validation on AddVmFromSnapshot

Added validation for source storage domains on AddVmFromSnapshotCommand
(i.e. source storage domains should be active).

Change-Id: I44ab14a527d2af7dce1b11b8d96f7e384c7b2027
Bug-Url: https://bugzilla.redhat.com/975114
Signed-off-by: Daniel Erez <derez@redhat.com>