revert deprecation of v2 API

For more info, see the openstack-dev mailing list:

    http://lists.openstack.org/pipermail/openstack-dev/2014-March/031016.html

Related Blueprint:

    https://blueprints.launchpad.net/keystone/+spec/deprecate-v2-api

Change-Id: Ic160da00f1c2fbcf0589b3e1c6c93f53a4e67b72
Merge "revert deprecation of v2 API"