Add specific doc build option and gate on warnings

Add doc venv to align with other OpenStack projejcts (such as keystone,
heat and nova-specs) who are using 'docs' for there doc builds.  Also
enable warnerrors in pbr to raise an error if there are any docs
formatting warnings.

Change-Id: Ifa31edf3c3392106a8aa1352bdd557bde2f1b9a1
Open Juno development

Bump version to 2014.2 to formally open Juno development. The
Icehouse release branch (milestone-proposed) will be cut from
the commit immediately preceding this one.

Change-Id: Id88e4d1b7a71c538cb430cb8e2fd0635840be237
Update comment for version to say "Juno" instead of "Icehouse"

Change-Id: I1372889411159ff1c3b26535e48022fe3dfbbbd9
Merge "Add specific doc build option and gate on warnings"