Add common utils

Taken from ceilometerclient. Will be useful for printing output and
importing versioned modules.
Add keystoneclient dependency
Add exceptions from ceilometerclient
Add API client code from ceilometerclient

Contains code for making http requests as well as very basic foundation
classes for resources and their managers.

Also adds FakeAPI and FakeResponse classes to test utils.
Add top level client wrapper module

Taken from ceilometerclient. It takes care of authentication via
keystoneclient and returns an authenticated and versioned client
instance.