contrib/asv.conf.json

test-merge-subrepos: make test compatible with chg

The test checks the output of '.hg/blackbox.log' which will contain
logs corresponding to chg in case chg is running. Therefore, this commit
modifies the test to take chg into consideration while checking the
blackbox.log contents.

Test Plan:
Ran the test 'test-merge-subrepos.t' with and without the '--chg'
option.

Differential Revision: https://phab.mercurial-scm.org/D925

{
    "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"
}