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
Adding Metadef Tag support

Adding rest api and db support for CRUD operations on the new
metadef_tags table.

Implements: https://blueprints.launchpad.net/glance/+spec/metadefs-tags
DocImpact

Change-Id: Icfa40555280ce69766381b0abe7ef399b806f6a0
Merge "Update config and docs for Multiple Containers"
Merge "Adding Metadef Tag support"