Change app.restapi to app.client_manager.session

This is step 1 toward using Keystone client's session.Session as the
primary session/requests interface in OSC.

* Move the session create into ClientManager and rename 'restapi' attribute to 'session'
* Set up ClientManager and session loggers
* Fix container and object command references to restapi/api

Change-Id: I013d81520b336c7a6422cd22c05d1d65655e64f8
Merge "Change app.restapi to app.client_manager.session"