Use virtualenv for Docker Python packages

[mwatts15]

Python packages repackaged by distro package maintainers are constrained mainly so that they work with other packages in the distro. Therefore, using such packages introduces unnecessary constraints in our Python software compared to using Python's conventional packaging format(s): wheels and source tarballs. Furthermore, to isolate our Python requirements from those of the operating system, a virtualenv is recommended.

This task is to replace the use of repackaged python libs in the Docker image with installations from wheels using pip in a virtualenv.