core: check vds status on resume paused VM

Checking whether the VDS that the VM is going to be resumed on is up was
missing when resuming a paused VM (regression).

Change-Id: Iac123f1758e5ed3dcedab335546df322fd76a0af
Bug-Url: https://bugzilla.redhat.com/1035667
Signed-off-by: Arik Hadas <ahadas@redhat.com>