core: new audit log for failed migration to server

The unused audit log VM_MIGRATION_FAILED_FROM_TO was renamed to
VM_MIGRATION_TO_SERVER_FAILED, and it is now used when migrate to server
fails.

Soon VM_MIGRATION_FAILED won't include the destination host, thus this
new audit log that does have the destination host is used for failed
migration to server instead.

Change-Id: I074836f713cc708c9b680bb2d6b3e99af17f66c3
Signed-off-by: Arik Hadas <ahadas@redhat.com>