Add auth_token_info to request context

The auth_token (and other) middleware adds a keystone.token_info value
to the request environment after validating the token.  We can pass this
value via the request context which allow us to avoid always re-requesting
another token in the keystoneclient instance in heat-engine.

Change-Id: Icac0e73fbddd5011fb41bd644036ba489189c405
Partial-Bug: #1317293
Merge "Add auth_token_info to request context"