Rename action state transitions (#677)

* Rename action state transitions

Now using active verbs as described in the design doc:

http://design.ros2.org/articles/actions.html#goal-states

Connects to ros2/rcl#399.

Signed-off-by: Jacob Perron <jacob@openrobotics.org>

rclcpp_action/include/rclcpp_action/server.hpp

@@ -360,7 +360,7 @@ protected:
       if (goal_handle) {
         resp = handle_cancel_(goal_handle);
         if (CancelResponse::ACCEPT == resp) {
-          goal_handle->_set_canceling();
+          goal_handle->_cancel_goal();
         }
       }
     }