Fix reference to middleware architecture doc

The auth_token docstring was referencing the middleware architecture
doc in keystoneclient. Updated to the new location.

Change-Id: I495bc332230f75e579e03c1b6f8feba49a26e5bf
Remove HTTP_X_STORAGE_TOKEN doc

This header isn't referenced in the code so remove it from the
documentation.

Change-Id: I77c5432d4d7a31422c75f9d675ec0e15f6c1164d
Merge "Fix reference to middleware architecture doc"
Merge "Remove HTTP_X_STORAGE_TOKEN doc"