Ignore SIGTERM when firing stop and signal.term

Move firing "server.stop" and "server.signal.term" triggers beyond
setting SIGTERM action to SIG_IGN in main().

This way handler commands for these triggers don't receive SIGTERM with
the rest of the process group and don't possibly terminate before doing
their work. E.g. snmptrap manages to send the notifications.
Merge pull request #823 from spbnick/trigger_with_ignored_sigterm

Ignore SIGTERM when firing stop and signal.term