Update IntegrationTestCase::_buildRequest

Hi,

I'm not sure it's the better way to do this but, the method is currently not use in this method.
I'm tried to test my controller. #4606

When i used __$this->put('/actions/changeStatus/1.json', ['status_id' => 2])__. But on the action of the controller, the request don't have a variable environment __REQUEST_METHOD__.

So these lines above resolve this problem.

Jason.