Updated openstack/openstack
Project: openstack/oslo.i18n  6392e9b6fcc96b88f2cd788f252047552df63c39

Add pbr to installation requirements

Add pbr to the list of installation requirements so that it is installed
via pip before this library is installed, instead of with easy_install.
This avoids issues like Bug #1384919, and ensures that projects that use
this library as a dependency are properly installed.

Change-Id: I6c155370dbd01fe4748d5137bdf288e8d3e1a67e