Add oslo.concurrency.

This is now required by Ironic. Initial RPM specs
here:

https://github.com/openstack-packages/python-oslo-concurrency

NOTE: There is an initial upstream doc fix that needs
to land before this will build:

 https://review.openstack.org/#/c/131862/

In order to build previously released versions we may need to
apply that patch. The upstream fix works fine w/ Delorean...
Merge pull request #9 from dprince/oslo.concurrency

Add oslo.concurrency.