Migrate to pbr for build

pbr is the libification of what was openstack.common.setup. If provides
the build information in a delcarative form, instead of as executable python
code, which works around the chicken and egg problem of needing setup
libraries present to run setup, but needing to run setup to tell if you
need setup libraries.

One of the features that comes along with this is versioning based on
git tags. If the current revision is a signed git tag, then that is the
version of the package. If it is not, the version is equal to the most
recent git tag, plus a commit count, plus a git sha (similar to git
describe, but scrubbed for python version rules compliance)

pbr updates are also part of the upcoming automation around ensuring
global requirements stay in sync.

Closes-Bug: #1179007
Change-Id: Ia473960be7e8aa44f09d48cea72ed3c8845f82fa
Merge "Migrate to pbr for build"