[S390] Enhanced handling of failed termination requests.

In case a request timed out and termination did not work, the console was
flooded with retry messages (every 1/10s). Now we use a 5s delay per retry and
generate a more precise message.

Signed-off-by: Horst Hummel <horst.hummel@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>