LP1204123 SIGTERM causes graceful shutdown (Perl)

LP1204123 SIGTERM causes graceful shutdown (Perl)

When sent the SIGTERM signal, listener processes will wait for all child
processes to complete their currently running tasks before killing all
child processes and exiting.

SIGQUIT and SIGINT can still be used for semi-graceful shutdowns, where
the listener de-registers and cleans up child processes, but does not
wait for child processes to finish their tasks.

To kill with fire, SIGKILL is still your friend.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>