Extend interface on InternalClient

 * add get_object
 * allow extra headers passthrough on HEAD/metadata reqeusts
 * expose (account|container|get_object)_ring properties

Pipeline propety access to the auto_create_account_prefix also allows us to
bypass the early exit on a container HEAD for auto_create_accounts if the
container-updater hasn't cycled yet.

Change-Id: I9b287d15f2426022d669d1186c9e22dd8ca13fb9
Merge "Extend interface on InternalClient" into feature/ec