S390: dont call system_shutdown on disabled wait

A disabled wait usually indicates a guest problem. Dont shutdown the
guest to allow guest dumping.
Have some special cases, e.g. a quiesce disabled wait. In that case
we want to shutdown.

Long term solution might be a crashed/panic indication.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
