Reap child processes gracefully if greenlet thread gets killed

If ProcessLauncher is run from within a thread we should be able to
call wait after the thread is killed to reap the child processes.
Catching this exception and then proceeding to the cleanup phase
accomplishes this.

Closes-Bug: #1282206
Change-Id: I9c863864c25c0478b720fc57cf0dccbe9bc9d9f6

openstack/common/service.py

@@ -384,19 +384,22 @@ def wait(self):
         LOG.debug('Full set of CONF:')
         CONF.log_opt_values(LOG, std_logging.DEBUG)
 
-        while True:
-            self.handle_signal()
-            self._respawn_children()
-            if self.sigcaught:
-                signame = _signo_to_signame(self.sigcaught)
-                LOG.info(_LI('Caught %s, stopping children'), signame)
-            if not _is_sighup_and_daemon(self.sigcaught):
-                break
-
-            for pid in self.children:
-                os.kill(pid, signal.SIGHUP)
-            self.running = True
-            self.sigcaught = None
+        try:
+            while True:
+                self.handle_signal()
+                self._respawn_children()
+                if self.sigcaught:
+                    signame = _signo_to_signame(self.sigcaught)
+                    LOG.info(_LI('Caught %s, stopping children'), signame)
+                if not _is_sighup_and_daemon(self.sigcaught):
+                    break
+
+                for pid in self.children:
+                    os.kill(pid, signal.SIGHUP)
+                self.running = True
+                self.sigcaught = None
+        except eventlet.greenlet.GreenletExit:
+            LOG.info(_("Wait called after thread killed.  Cleaning up."))
 
         for pid in self.children:
             try: