Make possible to set body in requesttoken requests in integration tests

"sendingAToWithRequesttoken" needs to be used to test some non OCS
endpoints which require the request token to be sent in the request. Now
it is possible to specify the body (or, rather, additional contents
beside the cookies and the request token) for those requests, as it will
be needed for example to upload an avatar.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>