SUBSCRIBE calls should use "application/recordio" Accept/Content-Type.

The agent operator API supports for "application/recordio" for things like attach-container-output, which streams objects back to the caller. I expected the master operator API SUBSCRIBE call to work the same way, w/ Accept/Content-Type headers for "recordio" and Message-Accept/Message-Content-Type headers for json (or protobuf). This was not the case.

Looking again at the master operator API documentation, SUBSCRIBE docs illustrate usage Accept and Content-Type headers for the "application/json" type. Not a "recordio" type. So my experience, as per the docs, seems expected. However, this is counter-intuitive since the whole point of adding the new Message-prefixed headers was to help callers consistently request (and differentiate) streaming responses from non-streaming responses in the v1 API.

Please fix the master operator API implementation to also support the Message-prefixed headers w/ Accept/Content-Type set to "recordio".

Observed on ubuntu w/ mesos package version 1.2.1-2.0.1