The Admin Guide now contains information about the ring serialization
change (and importantly, how to downgrade, if necessary).
Also added container-server conf var, "allow_versions" to the Deployment
Guide.
Also changed description of proxy-server conf var,
"max_containers_whitelist" to say it contains "account names" not
"account hashes".
Change-Id: Ib23c6118cc5195cc04765afd28e442e4c735f0d4