Move to pbr freeze from pip freeze

For the things that use pbr, we no longer have git shas in the version
numbers. So, in order to verify what exact version of things we're
installing, use pbr freeze to collect the information.

Change-Id: I41ff993aa86e6a7ac1beed3cc5a3b94dcadbdd7c
Merge "Move to pbr freeze from pip freeze"