Adjust the behavior of the cancel action

For pending and waiting jobs this should set the cancel status
immediately. For running jobs it should just set the cancel flag and let
the running job set the cancelled status itself during its cancelation
procedure.  This also prevents a race condition where the task manager
will start dependent jobs before realizing the status is cancelled.

awx/main/models/unified_jobs.py

@@ -783,8 +783,11 @@ class UnifiedJob(PolymorphicModel, PasswordFieldsModel, CommonModelNameNotUnique
         if self.can_cancel:
             if not self.cancel_flag:
                 self.cancel_flag = True
-                self.status = 'canceled'
-                self.save(update_fields=['cancel_flag', 'status'])
+                cancel_fields = ['cancel_flag']
+                if self.status in ('pending', 'waiting'):
+                    self.status = 'canceled'
+                    cancel_fields.append('status')
+                self.save(update_fields=cancel_fields)
                 self.socketio_emit_status("canceled")
             if settings.BROKER_URL.startswith('amqp://'):
                 self._force_cancel()