util: softsig version of function to setup logging signal handlers

util: softsig version of function to setup logging signal handlers

Provide a new routine to setup the server log signals which registers
soft signal handlers for the common log management signals (SIGTSTP and
SIGHUP). Keep the old SetupLogSignals() routine around while lwp still
exists.

Change-Id: Ic9151c7ad25528e8e4008a4567836e4196cbe8c3
Reviewed-on: https://gerrit.openafs.org/12238
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>