Python coverage

Upgrading rules_python in Bazel and running tests again version 0.36.0 showed problems with coverage support.

To reproduce run `bazel test //src/test/shell/bazel:bazel_coverage_hermetic_py_test` from Bazel repository. It fails saying the test has failed, but this previously with builtin Python rules wasn't the case.

I went down the rabbit hole, but I couldn't figure it out. I think that this test should be moved out of Bazel into rules_python, if it isn't already.