Merge branch 'dl/test-must-fail-fixes-6' into master

Dev support to limit the use of test_must_fail to only git commands. * dl/test-must-fail-fixes-6: test-lib-functions: restrict test_must_fail usage t9400: don't use test_must_fail with cvs t9834: remove use of `test_might_fail p4` t7107: don't use test_must_fail() t5324: reorder `run_with_limited_open_files test_might_fail` t3701: stop using `env` in force_color()