tests: conditionalize color output on abort
This broke in
afc4ad706f9c. I'm not sure why other aborts don't need to be
conditionalized, but `hg help foo` does abort in red for both msys and cmd.exe.
{
"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"
}