Catch exceptions from worker controller.

Surprise exceptions can get hidden by the Gearman stuff. Catch them
here and report failure.

Change-Id: I7fab24d809f8e91bc68c45296f369011e4d5c30d

libra/worker/controller.py

@@ -45,6 +45,8 @@ class LBaaSController(object):
 
         action = self.msg[self.ACTION_FIELD].upper()
         self.logger.info("Requested action: %s" % action)
+
+        try:
             if action == 'CREATE':
                 return self._action_create()
             elif action == 'UPDATE':
@@ -60,6 +62,11 @@ class LBaaSController(object):
                                   (self.ACTION_FIELD, action))
                 self.msg[self.RESPONSE_FIELD] = self.RESPONSE_FAILURE
                 return self.msg
+        except Exception as e:
+            self.logger.error("Controller exception: %s, %s" %
+                              (e.__class__, e))
+            self.msg[self.RESPONSE_FIELD] = self.RESPONSE_FAILURE
+            return self.msg
 
     def _action_create(self):
         """