Fix references to auth_token in middlewarearchitecture doc

The middlewarearchitecture doc was still referring to
keystone.middleware.auth_token, but the middleware was moved to
keystoneclient.

Also, corrected some other minor typos.

Change-Id: I270ea2ccc739596e99a4a852bff3b5b7d1c85c82
Merge "Fix references to auth_token in middlewarearchitecture doc"