tests/sitecustomize.py

py3: fix broken man page generation, it was generating `(default: NUL*)`

`bytes(default)` was producing things like `(default: \x00)` when handed
non-bytes values such as `1`, `10`, or `True`. The man page generation would
apparently ignore these bytes and produce man pages that had the string
`(default: )`.

Test Plan:
- Ran `cd doc; python3 gendoc.py "hg.1.gendoc"` and grepped for bad output
- Ran `make deb`, extracted the deb, manually inspected `hg.1` file.

Differential Revision: https://phab.mercurial-scm.org/D8639

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