Stop all collectors on signal

This ensures that we stop all collectors at the start of the
exit signal handlers.  This helps prevent restarting the client
after the threads have been asked to stop.

aprsd/main.py

@@ -72,6 +72,7 @@ def main():
 
 def signal_handler(sig, frame):
     click.echo('signal_handler: called')
+    collector.Collector().stop_all()
     threads.APRSDThreadList().stop_all()
     if 'subprocess' not in str(frame):
         LOG.info(