[pantsd] Integration tests under chroot are broken with pantsd

[blorente]

Problem

In CI, we run a cron job every day to check that master runs. In that cron job, we run the same integration test shards with and without pantsd.
Since we started introducing integration tests under chroot, those shards have been broken.
The main problem seems to be that Watchman behaves baldly under chroot (relevant thread).
As far as we know, these are the concrete problems:

• When using with chroot, the watchman socket path ends up being too long.
• When using with chroot, the folder we chroot to seems to dissapear before we properly close out pantsd, crashing watchman.

Repro

Run integration tests with the flag --test-pytest-chroot and the environment variable USE_PANTSD_FOR_INTEGRATION_TESTS="true"