Update config and docs for Multiple Containers

This adds appropriate config options to reflect
changes in the Multiple Containers spec.

Approved spec:
 https://review.openstack.org/#/c/124522

DocImpact
bp: swift-store-multiple-containers
Change-Id: Ia6b4cb215c4945fb0373e9af5358725209353aa8
Merge "Update config and docs for Multiple Containers"