core: fix log when detecting HA VM went down

The previous log message noted that there was an error while starting
the VM everytime the monitoring detects that HA VM went down. This might
be wrong since the VM might already be UP before it went down. Thus,
this patch corrects the log message.

Change-Id: I563d914d9adfa7e555b1c5d21d39c10d5b1d4b41
Signed-off-by: Arik Hadas <ahadas@redhat.com>