Fix ResourceActionNotSupported errors in log

In 37ef669705 (in Kilo) we made signalling
a resource asynchronous because things like e.g. scaling an autoscaling
group were too slow to do synchronously (bug 1394095).

However, for resources that don't have a handle_signal() method at all,
this means that if a signal other than one handled by Heat (e.g. to
clear a hook) is received then the user won't be notified of the error.
There will instead be an error message in the logs warning of an
unhandled exception in a thread.

(Previously, similar problems occurred if the user was attempting to
clear a hook and some error occurred. This has since been fixed as bug
1472515, in Liberty.)

If there's no handle_signal() method defined, then calling
Resource.signal() is quick (i.e. it's only going to clear a hook, or
raise an error). So handle this case synchronously. This ensures that
any error is reported to the user and not in the log.

Change-Id: I917b4c7d4ab2cde46148197a3a232d5dc70f63d7
Related-Bug: #1472515

heat/engine/service.py

@@ -1872,12 +1872,13 @@ class EngineService(service.ServiceBase):
         if callable(rsrc.signal):
             rsrc._signal_check_action()
             rsrc._signal_check_hook(details)
-            if sync_call:
+            if sync_call or not callable(getattr(rsrc, 'handle_signal', None)):
                 _resource_signal(stack, rsrc, details, False)
-                return rsrc.metadata_get()
             else:
                 self.thread_group_mgr.start(stack.id, _resource_signal,
                                             stack, rsrc, details, False)
+            if sync_call:
+                return rsrc.metadata_get()
 
     @context.request_context
     def resource_mark_unhealthy(self, cnxt, stack_identity, resource_name,

heat_integrationtests/api/gabbits/resources.yaml

@@ -82,7 +82,7 @@ tests:
 
 - name: signal resource
   POST: $LAST_URL/signal
-  status: 200
+  status: 400
 
 - name: delete stack with resources
   DELETE: /stacks/$ENVIRON['PREFIX']-rsrcstack