core: assure migration jobs are completed

Add missing call to failedToRunVm method when VM migration fails because
the VM went down on the destination and source during the migration,
this call assures that the migration job is completed in this case as
well.

Change-Id: Iee82fc63b09d53e085fe32c710b43b5cc9b1498b
Bug-Url: https://bugzilla.redhat.com/952147
Signed-off-by: Arik Hadas <ahadas@redhat.com>