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: Ie83440251779d49b83747a51111a89edccc88f9c
Signed-off-by: Ofri Masad <omasad@redhat.com>