Replace HttpConnection in auth_token with Requests
Replace HttpConnection in auth_token with Requests

Requests is becoming the standard way of doing http communication, it
also vastly simplifies adding other authentication mechanisms. Use it in
the auth_token middleware.

This adds the ability to specify a CA file that will be used to verify a
HTTPS connections or insecure to specifically ignore HTTPS validation.

SecurityImpact
DocImpact
Partial-Bug: #1188189
Change-Id: Iae94329e7abd105bf95224d28f39f4b746b9eb70

varunarya10/keystonemiddleware