Prevent coverage reporting issues in tmp dir

Pytorch generates some python files in the tmp dir and executes them; coverage
then fails due to not being able to find the source files. We pass a flag to
omit the tmp dir from coverage reporting.

Commit: 6ff10ae
Branch: https://github.com/bazeltools/rules_python/tree/patch-tmp-coverage-1.6.1

This approach is from the discussion in
bazel-contrib#2599 (comment)

Author: jklukas

python/private/python_bootstrap_template.txt

@@ -471,6 +471,11 @@ source =
     kparams['stdout'] = sys.stderr
     kparams['stderr'] = sys.stderr
 
+  # Prevent coveragepy report issues when packages execute files in tmp dir.
+  import tempfile
+  omit_pattern = os.path.join(tempfile.gettempdir(), "*")
+  params.append(f'--omit={omit_pattern}')
+
   lcov_ret_code = subprocess.call(
     params,
     **kparams