Fix coverity check FORWARD_NULL error

Change-Id: I1e115003748b8c73144984c7132845a083b5d2a2

heat/common/exception.py

@@ -336,7 +336,7 @@ class ResourceFailure(HeatExceptionWithPath):
                 path = res_path
         else:
             self.exc = None
-            res_failed = 'Resource %s failed: ' % action.upper()
+            res_failed = 'Resource %s failed: ' % self.action.upper()
             if res_failed in exception_or_error:
                 (error, message, new_path) = self._from_status_reason(
                     exception_or_error)

heat/engine/resources/aws/ec2/instance.py

@@ -558,6 +558,7 @@ class Instance(resource.Resource, sh.SchedulerHintsMixin):
             if server is not None:
                 self.resource_id_set(server.id)
 
+        assert server is not None
         creator = progress.ServerCreateProgress(server.id)
         attachers = []
         for vol_id, device in self.volumes():

heat/engine/resources/openstack/nova/server.py

@@ -884,6 +884,7 @@ class Server(server_base.BaseServer, sh.SchedulerHintsMixin,
             if server is not None:
                 self.resource_id_set(server.id)
 
+        assert server is not None
         return server.id
 
     def check_create_complete(self, server_id):