tests/sitecustomize.py

run-tests: do not inherit file descriptor when running a command

This is one of the difference between python2 and python3 and could have been a
reason why test hang with python2 + chg. This does not seems to help the
hanging issue at all…

However, now that this is written lets reduce the difference between python2
and python3.

Differential Revision: https://phab.mercurial-scm.org/D11226

from __future__ import absolute_import
import os

if os.environ.get('COVERAGE_PROCESS_START'):
    try:
        import coverage
        import uuid

        covpath = os.path.join(
            os.environ['COVERAGE_DIR'], 'cov.%s' % uuid.uuid1()
        )
        cov = coverage.coverage(data_file=covpath, auto_data=True)
        cov._warn_no_data = False
        cov._warn_unimported_source = False
        cov.start()
    except ImportError:
        pass