some pure-http migration. Still need tests for the worker changes.

Conflicts:
	otter/worker/launch_server_v1.py
simplify the auth code:

- just add an invalidate() method, no refresh= argument to authenticate_tenant
- add an ICachingAuthenticator interface and declare that the CachingAuthenticator implements it.
add test for invalidate method
lint/docs
:data:`None`
Merge pull request #697 from rackerlabs/invalidate-auth-cache

Add ICachingAuthenticator with 'invalidate' method