Centrally register stack dump handler

We want the stack dump handler to be present in all zuul apps so this
can be registered in a central place.

Change-Id: I0c4a97d6ee983aa4d57928682dfb6eeffd050197

zuul/cmd/__init__.py

@@ -176,6 +176,10 @@ class ZuulDaemonApp(ZuulApp):
         pid_fn = self.getPidFile()
         pid = pid_file_module.TimeoutPIDLockFile(pid_fn, 10)
 
+        # Early register the stack dump handler for all zuul apps. This makes
+        # it possible to also gather stack dumps during startup hangs.
+        signal.signal(signal.SIGUSR2, stack_dump_handler)
+
         if self.args.nodaemon:
             self.run()
         else:

zuul/cmd/executor.py

@@ -130,8 +130,6 @@ class Executor(zuul.cmd.ZuulDaemonApp):
                                        log_streaming_port=self.finger_port)
         self.executor.start()
 
-        signal.signal(signal.SIGUSR2, zuul.cmd.stack_dump_handler)
-
         if self.args.nodaemon:
             signal.signal(signal.SIGTERM, self.exit_handler)
             while True:

zuul/cmd/merger.py

@@ -62,8 +62,6 @@ class Merger(zuul.cmd.ZuulDaemonApp):
                                                      self.connections)
         self.merger.start()
 
-        signal.signal(signal.SIGUSR2, zuul.cmd.stack_dump_handler)
-
         if self.args.nodaemon:
             signal.signal(signal.SIGTERM, self.exit_handler)
             while True:

zuul/cmd/scheduler.py

@@ -123,7 +123,6 @@ class Scheduler(zuul.cmd.ZuulDaemonApp):
         import zuul.webapp
         import zuul.zk
 
-        signal.signal(signal.SIGUSR2, zuul.cmd.stack_dump_handler)
         if (self.config.has_option('gearman_server', 'start') and
             self.config.getboolean('gearman_server', 'start')):
             self.start_gear_server()

zuul/cmd/web.py

@@ -106,8 +106,6 @@ class WebServer(zuul.cmd.ZuulDaemonApp):
 
         self.configure_connections()
 
-        signal.signal(signal.SIGUSR2, zuul.cmd.stack_dump_handler)
-
         try:
             self._run()
         except Exception: