incomplete
possibly cleaner
split out retry and auth in separate func - not working
Merge branch 'master' into cache_our_token
working with tests
Logging when getting token
failure cases return UpstreamError
retry_on_unauth tests
docs corrected
better log - thanks @cyli
sample auth raises different exception - thanks @cyli

Also, added test to ensure that auth errors are propogated
correct assertion
Merge pull request #716 from rackerlabs/cache_our_token

AS-290: ImpersonatingAuthenticator caches token