t0017: clarify dubious test set-up

1ff750b1 (tests: make GIT_TEST_GETTEXT_POISON a boolean, 2019-06-21) added this test, in which "test-tool -C" is fed a name of a directory that does not exist, and expects that it dies because of a failure to read the configuration file(s), because the configuration setting is screwed up to contain mutual inclusion loop, before it notices that the directory to chdir into does not exist and dies. It is of dubious value to etch the current order of events, i.e., the configuration needs to be read that early (for initializing trace2 subsystem) before we even notice the lack of the directory and have a chance to fail, into stone. Indeed, if you completely compile out trace2 subsystem so that it does not even attempt to read the configuration that early, we would die with a different error message (i.e. "unable to chdir to 'cycle'") and this test will fail. At least give a bogus argument to "test-tool -C" a name that is clearly bogus to make sure we can more easily see what is going on with plenty of comments. We may want to remove this test altogether, instead, though. Signed-off-by: Junio C Hamano <gitster@pobox.com>