Updated OpenStackClient class.
* Added snapshot manager.
* Fixed volume manager.
Updated BaseManager class and BaseResource class.
* Removed dict emulation from BaseResource.
* Removed six from BaseManager and BaseResource.
* Renamed http_* methods to * in BaseResource.
* Made BaseResource hold BaseManager instance.
Updated BaseSession Class.
* Added endpoint_type argument for each HTTP method.
Updated http_utils module.
* Renamed get() as get_raw() and get_json() as get().
* Renamed put() as put_raw() and put_json() as put().
* Renamed post() as post_raw() and post_json() as post().
Updated keystone_v2 session manager module.
* Added HTTP request methods.
* Removed JSON-related headers because HTTP methods in http_utils do.
Updated volume modules.
* Fixed many bugs.
* Implemented create() and update() in cinder_v2 module.
Updated snapshot driver.
* Fixed many bugs.
* Implemented create() and update() in cinder_v2.