Don't pass empty action strings to ceilometer

Note: this only really happens when using the cloud watch
resource template.

Partial-bug: #1373247
Change-Id: I084d28dfbbd0f2d7a6a18a09600f86880fa394d5

heat/engine/resources/ceilometer/alarm.py

@@ -84,7 +84,8 @@ def actions_to_urls(stack, properties):
                     url = stack[act].FnGetAtt('AlarmUrl')
                     kwargs[k].append(url)
                 else:
-                    kwargs[k].append(act)
+                    if act:
+                        kwargs[k].append(act)
         else:
             kwargs[k] = v
     return kwargs