Allow OpenStack services to use a python venv

There are two problems that we need to start anticipating:

  * Some OpenStack services are running on physical hosts in the root
    namespace. This creates a situation where it's possible for a service to
    have conflicting requirements with what is already on the host installed
    through the host package manager. In these situation we've found some
    instabilities that needed workarounds to ensure there are no stability or
    usage issues with the service.

  * OpenStack services have started moving toward a non-integrated release
    which will allow projects to change their release cycle / cadence which
    will effect versions of services that we deploy. Additionally, these
    projects may choose to use dependencies outside of what is set in Global
    requirements.

The use of on metal services, the change in release cycles / cadence, and
the likelihood of projects using requirements that conflict with one another
requires more separation between the installed projects which lends itself
to using a virtual environment for installed OpenStack Python code.