Make auth_token middleware fetching respect prefix
Make auth_token middleware fetching respect prefix

In auth_token middleware auth_prefix is only added to requests that go
through the _json_request method. This doesn't include the two
certificate fetching functions. Manually add the auth_prefix to both
those requests.

Closes-Bug: #1211615
Change-Id: I25d1b401598c9a443ddef0fc3259ba859aee8c76

varunarya10/keystonemiddleware