Python PATH is Broken on Mac High Sierra

[liangfok]

See the errors here:

https://drake-jenkins.csail.mit.edu/view/Nightly%20Production/job/mac-high-sierra-unprovisioned-clang-bazel-nightly-release/35/

env: python2: No such file or directory
...
//:py/install_test                                                       FAILED in 0.9s

This is likely due to a Bazel update. An RC file likely needs the following to be added:

--action_env=PATH=/usr/local/bin:/usr/bin:/bin

[jamiesnape]

Relates bazelbuild/bazel#6648.

[EricCousineau-TRI]

Would adding this to install_prereqs_user_environment for Mac make it work?

[jamiesnape]

It would, though technically this is not a Mac issue.

[jamiesnape]

I imagine the analog for Linux would be --action_env=PATH=/usr/bin:/bin.

[jamiesnape]

I think this also makes our own version of the bzl which() function redundant, but that is not going to break anything.

[jwnimmer-tri]

I think this also makes our own version of the bzl which() function redundant, but that is not going to break anything.

Not quite?

(1) When our //tools/workspace rules are used from a bazel_drake_external, we don't know what the action $PATH will be. I think its still good to ignore whatever the user configured, at least by default.

(2) I'm not sure that rcfile build --action_env affects, e.g., bazel fetch //....