Fixes #4878: Proxy requests to guestid and content_overrides to candlepin

- Add support for proxing PUT requests to candlepin

- Allow proxying DELETE request with body to candlepin

- Proxy calls to /api/consumer/:id/guestids/* directly to candlepin
  * Add fake root path for guestids allowing client tooling to check support
  * Proxy GET /consumers/:id/guestids to candlepin
  * Proxy GET /consumers/:id/guestids/:guest_id to candlepin
  * Proxy PUT /consumers/:id/guestids to candlepin
  * Proxy PUT /consumers/:id/guestids/:guest_id to candlepin
  * Proxy DELETE /consumers/:id/guestids/:guest_id to candlepin

- Proxy requests to candlepin's content_overrides
  * Added fake root path that is checked by rhsm (unlocks adding extra
    guest data support in python-rhsm)
  * GET /api/consumers/:id/content_overrides
  * PUT /api/consumers/:id/content_overrides
  * DELETE /api/consumers/:id/content_overrides
Merge pull request #3884 from mstead/proxy-candlepin-requests

Proxy requests to candlepin for guest ids and content overrides API calls