test-extension: flush diagnostic message to stabilize chg output
Since chg server may create new file object for the attached stdout,
procutil.stdout is not ui.fout and the buffered procutil.stdout data wouldn't
be flushed at all. That's why test-extension.t passes without modification
on Python 2.
{
"version": 1,
"project": "mercurial",
"project_url": "https://mercurial-scm.org/",
"repo": "..",
"branches": ["default", "stable"],
"environment_type": "virtualenv",
"show_commit_url": "https://www.mercurial-scm.org/repo/hg/rev/",
"benchmark_dir": "benchmarks",
"env_dir": "../.asv/env",
"results_dir": "../.asv/results",
"html_dir": "../.asv/html"
}