test-lib: --valgrind should not override --verbose-log

The --verbose test option cannot be used with test harnesses like "prove". Instead, you must use --verbose-log. Since the --valgrind option implies --verbose, that means that it cannot be used with prove. I.e., this does not work: prove t0000-basic.sh :: --valgrind You'd think it could be fixed by doing: prove t0000-basic.sh :: --valgrind --verbose-log but that doesn't work either, because the implied --verbose takes precedence over --verbose-log. If the user has given us a specific option, we should prefer that. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>