git p4 test: check for error message in failed test

Make sure the test fails for the expected reason.

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9800-git-p4-basic.sh

@@ -45,7 +45,8 @@ test_expect_success 'git p4 sync uninitialized repo' '
 	test_when_finished cleanup_git &&
 	(
 		cd "$git" &&
-		test_must_fail git p4 sync
+		test_must_fail git p4 sync 2>errs &&
+		test_i18ngrep "Perhaps you never did" errs
 	)
 '