vm: report exit reason if restore state fails

The exit reason code needs to be reported an all error paths.
It was mistakenly left out on the restoreState error path,
most likely because this path is different because the exitMessage
is overwritten.

This patch ensures exitReason is always reported.

Change-Id: Ifda6852e5d91cfb17d8c7c2d6a0997346854ec83
Signed-off-by: Francesco Romani <fromani@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27703
Reviewed-by: Dan Kenigsberg <danken@redhat.com>