websockify does not react to SIGTERM

Child processes are not terminated when parent process of websockify
is killed.

In this fix made provision to terminate all child processes when
parent process is killed.

Fixes #138

websockify/websocket.py

@@ -1079,6 +1079,16 @@ class WebSocketServer(object):
 
                     except (self.Terminate, SystemExit, KeyboardInterrupt):
                         self.msg("In exit")
+                        # terminate all child processes
+                        if multiprocessing and not self.run_once:
+                            childs = multiprocessing.active_children()
+
+                            for child in childs:
+                                pid = child.pid
+                                if pid != os.getpid():
+                                    self.msg("Terminating child %s" % pid)
+                                    os.kill(pid, signal.SIGTERM)
+
                         break
                     except Exception:
                         exc = sys.exc_info()[1]