fix a bug that breaks job cancel on single node jobs

1.  Install awx w/ a single node.
2.  Start a long-running job.
3.  Forcibly kill the `awx-manage run_dispatcher` process (e.g.,
    SIGKILL) and do not start it again.
4.  The job remains in running - without a second cluster to discover
    the job, it is never reaped.
5.  This PR allows you to cancel the job from the UI+API.

awx/main/models/workflow.py

@@ -481,3 +481,9 @@ class WorkflowJob(UnifiedJob, WorkflowJobOptions, SurveyJobMixin, JobNotificatio
     @property
     def preferred_instance_groups(self):
         return []
+
+    @property
+    def actually_running(self):
+        # WorkflowJobs don't _actually_ run anything in the dispatcher, so
+        # there's no point in asking the dispatcher if it knows about this task
+        return self.status == 'running'