swift: add container sync

The basic concepts of container synchronization are outlined here:
http://docs.openstack.org/developer/swift/overview_container_sync.html

This part takes care of enabling container sync in the proxy pipeline and
distribute the credentials to the proxy and container servers.

A separate utility will take care of enabling synchronization on a
per-container basis.

Change-Id: Ie771a29aa5e99757301f5f7a6ffafda7528e8f55