Migrate to PBR for build tooling.

pbr is the library-ified version of the code that was in
openstack.common.setup and version. It builds on top of d2to1 to
provide declarative build configuration.

Change-Id: Ic264fa33e17fe5fdc71d8c53412495b069ab74a4
Merge "Migrate to PBR for build tooling."