Outdent subtest intro comment

This commit puts the subtest intro comment at the parent indent level.

Before:

    ok 1 - regular test
        # Subtest: my first subtest
        ok 1 - first test
        ok 2 - second test
        ok 3 - third test
        1..3
    ok 2 - my first subtest

After:

    ok 1 - regular test
    # Subtest: my first subtest
        ok 1 - first test
        ok 2 - second test
        ok 3 - third test
        1..3
    ok 2 - my first subtest

I think this is much easier to read because it brackets the subtest
information at the same indentation level.  The subtest details are
clearly between the opening comment and the matching "ok".