metrics uses cachingauthenticator
generate_authenticator api.py -> auth.py
Implements interface matcher
using otter.auth.generate_authenticator in metrics
Merge branch 'master' into metrics_cache_auth

Conflicts:
	otter/auth.py
	otter/metrics.py
	otter/tap/api.py
	otter/test/tap/test_api.py
	otter/test/test_auth.py
	otter/test/test_metrics.py
removed redef occurred after merge conflict fix
s/Implements/Provides - thanks @lvh
Merge pull request #743 from rackerlabs/metrics_cache_auth

Metrics uses CachingAuthenticator