We have some dependencies that are often problematic to install and not

sufficient for some of our tests. Namely, Bazaar/Breezy and Mercurial.

While these can install in a Python virtual environment, they still need

to be installed system-wide for SSH-based tests. Having both installed

can lead to inconsistent results. Because of this, it's better to just

require installing them system-wide.
We also no longer upgrade pip and setuptools. This used to be needed

back when these were heavily transitioning to modern packaging

capabilities in the Python 2 era. Nowadays they do more harm than good,

particularly with some pip bugs that can remove incorrect versions of

the pipX.Y scripts.

Successfully installed packages in a brand-new development environment.