core: Add event logs for balloon issues

Added AuditLog for two cases:
 - balloon is requested but the balloon driver on the VM is not
   responding.
 - balloon is inflated but MOM lost control over the balloon device
   (caused by guest agent failure).

Change-Id: I30395b90b74777eacca76419c20960eb812204ae
Signed-off-by: Ofri Masad <omasad@redhat.com>