Provide logging messages in ipcluster log when engine or controllers fail to start (chapmanb/bcbio-nextgen#298

IPython/parallel/apps/ipclusterapp.py

@@ -348,7 +348,11 b' class IPClusterEngines(BaseParallelApplication):'
         # Some EngineSetLaunchers ignore `n` and use their own engine count, such as SSH:
         n = getattr(self.engine_launcher, 'engine_count', self.n)
         self.log.info("Starting %s Engines with %s", n, self.engine_launcher_class)
+        try:
         self.engine_launcher.start(self.n)
+        except:
+            self.log.exception("Engine start failed")
+            raise
         self.engine_launcher.on_stop(self.engines_stopped_early)
         if self.early_shutdown:
             ioloop.DelayedCallback(self.engines_started_ok, self.early_shutdown*1000, self.loop).start()
@@ -517,7 +521,11 b' class IPClusterStart(IPClusterEngines):'
     def start_controller(self):
         self.log.info("Starting Controller with %s", self.controller_launcher_class)
         self.controller_launcher.on_stop(self.stop_launchers)
+        try:
         self.controller_launcher.start()
+        except:
+            self.log.exception("Controller start failed")
+            raise
 
     def stop_controller(self):
         # self.log.info("In stop_controller")