fix: set PYTHONNOUSERSITE

[froody]

Set PYTHONNOUSERSITE to prevent adding user directories outside bazel. I found a py_test run with bazel test was importing modules from ~/.local/lib/python3.10/site-packages/ which allowed it to run successfully on my machine but fail on other hosts.

Before:

USER_SITE directory in sys.path when running python code via
bazel run or bazel test

After:

sys.path only contains paths relative to the bazel-out directory

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[rickeylev]

Hi @froody, thanks for your contribution!

I think this is a good idea, so +1 overall setting this. Changes needed to merge:

• Pass -s to the interpreter instead of an environment variable. envvars contaminate subprocesses, which is undesirable.
• Please update the bootstrap=script impl. i.e update python/private/stage1_bootstrap_template.sh to pass -s too
• Please update CHANGELOG.md and add an entry under Changed.
• We'll need tests. Have a look at tests/bootstrap_impls. I think you can copy/paste run_binary_zip_no_test, modify bin.py to print out sys.flags.no_user_site, and check the value in run_binary_zip_no_test.sh

I'm pretty certain this is gonna break something about some user's workflow, though I don't know what that would be.

[aignas]

I would also like to see the behaviour switched based on a config flag so that users that need to opt out from the behaviour can do so.

Defaulting to always including -s should be good enough.