Allow other clients to use the Session

The session object was built as greenfields as possible, trying to make decisions based on the best outcomes rather than what the current state of clients is (with some exceptions).

Now that it's there there will need to be some considerations made to allowing the session to work with existing clients in a way that maintains compatibility with there current operations.

This blueprint includes the helper functions that are part of keystoneclient that are mostly needed for other clients.

For example the session adapter is a wrapper to help other clients use a session object and manage the parameters that can be passed. keystoneclient will end up using this to be consistent - but it's mostly for other clients.