alarms: add logging and peaceful exit for logback startup errors

If there is an runtime exception from the configuration of the
SimpleSocketServer it is currently not handled, causing
repeated restart of the domain.

This patch catches and logs the exception, but does not rethrow it.

Target: master
Patch: http://rb.dcache.org/r/6720
Require-notes: no
Require-book: no
Acked-by: Gerd