Remove SCM command line tool dependencies and stop upgrading pip/setuptools.

Review Request #12718 — Created Nov. 10, 2022 and submitted — Latest diff uploaded


Review Board


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.