I noted in the test log that psutil is being installed twice:

[task 2019-11-14T06:32:13.049Z] 06:32:13     INFO -  Collecting psutil>=3.1.1
[task 2019-11-14T06:32:14.009Z] 06:32:14     INFO -    Downloading https://pypi.pub.build.mozilla.org/pub/psutil-5.6.3.tar.gz (435kB)
[task 2019-11-14T06:32:15.377Z] 06:32:15     INFO -  Building wheels for collected packages: psutil
[task 2019-11-14T06:32:15.379Z] 06:32:15     INFO -    Running setup.py bdist_wheel for psutil: started
[task 2019-11-14T06:32:19.590Z] 06:32:19     INFO -    Running setup.py bdist_wheel for psutil: finished with status 'done'
[task 2019-11-14T06:32:19.593Z] 06:32:19     INFO -    Stored in directory: /builds/worker/.cache/pip/wheels/3a/fc/dc/db9dcea242913b6150a848d3cfe9036ca192299697e933e413
[task 2019-11-14T06:32:19.609Z] 06:32:19     INFO -  Successfully built psutil
[task 2019-11-14T06:32:19.609Z] 06:32:19     INFO -  Installing collected packages: psutil
[task 2019-11-14T06:32:19.743Z] 06:32:19     INFO -  Successfully installed psutil-5.6.3
[task 2019-11-14T06:32:19.784Z] 06:32:19     INFO - Return code: 0

then

[task 2019-11-14T06:32:37.858Z] 06:32:37     INFO - Copy/paste: /builds/worker/workspace/build/venv/bin/pip install --timeout 120 --no-index --find-links https://pypi.pub.build.mozilla.org/pub psutil==5.4.3
[task 2019-11-14T06:32:37.859Z] 06:32:37     INFO - Using env: (same as previous command)
[task 2019-11-14T06:32:38.016Z] 06:32:38     INFO -  Ignoring indexes: https://pypi.python.org/simple
[task 2019-11-14T06:32:38.022Z] 06:32:38     INFO -  Collecting psutil==5.4.3
[task 2019-11-14T06:32:38.654Z] 06:32:38     INFO -    Downloading https://pypi.pub.build.mozilla.org/pub/psutil-5.4.3.tar.gz (412kB)
[task 2019-11-14T06:32:38.994Z] 06:32:38     INFO -  Building wheels for collected packages: psutil
[task 2019-11-14T06:32:38.995Z] 06:32:38     INFO -    Running setup.py bdist_wheel for psutil: started
[task 2019-11-14T06:32:39.941Z] 06:32:39     INFO -    Running setup.py bdist_wheel for psutil: finished with status 'done'
[task 2019-11-14T06:32:39.943Z] 06:32:39     INFO -    Stored in directory: /builds/worker/.cache/pip/wheels/80/3b/7d/50d02fa834e4d74ba3c01a3ae8a3f8b61edeba6b2dad895e79
[task 2019-11-14T06:32:39.958Z] 06:32:39     INFO -  Successfully built psutil
[task 2019-11-14T06:32:39.958Z] 06:32:39     INFO -  Installing collected packages: psutil
[task 2019-11-14T06:32:39.959Z] 06:32:39     INFO -    Found existing installation: psutil 5.6.3
[task 2019-11-14T06:32:39.968Z] 06:32:39     INFO -      Uninstalling psutil-5.6.3:
[task 2019-11-14T06:32:39.979Z] 06:32:39     INFO -        Successfully uninstalled psutil-5.6.3
[task 2019-11-14T06:32:40.122Z] 06:32:40     INFO -  Successfully installed psutil-5.4.3
[task 2019-11-14T06:32:40.166Z] 06:32:40     INFO - Return code: 0

Log: https://firefoxci.taskcluster-artifacts.net/ffvSsCpqS-KpF23ddOa46g/0/public/logs/live_backing.log

This seems wasteful since we're doing two operations for no reason.

Given that we have vendored (in-tree and in our internal pypi mirror) psutil 5.6.3, why not just standardize on this one version?

https://hg.mozilla.org/mozilla-central/rev/7a28e398b881