Using the latest depot_tools no longer works. depot_tools also wants
to auto-update itself, which must now be disabled.
We also need to disable the copy of python (vpython) included in
depot_tools, since for some distros, it has dependencies on system
libraries that no longer exist.
Finally, we need to force some distros to use python 2, because our
build system is ancient and needs to be ripped out and replaced some
day soon.
This fixes build issues in our CI, our Dockerfiles, and in general on
certain platforms or distros.
Closes#1023
3fd538a587