sharness: t0030-mount output known breakage

The test_must_fail check fails on osx. (it does not seem to fail on
linux). See #1109

test/sharness/t0030-mount.sh

@@ -24,7 +24,7 @@ test_expect_success "'ipfs mount' fails when there is no mount dir" '
 	test_must_fail ipfs mount -f=not_ipfs -n=not_ipns >output 2>output.err
 '
 
-test_expect_success "'ipfs mount' output looks good" '
+test_expect_failure "'ipfs mount' output looks good" '
 	test_must_be_empty output &&
 	test_should_contain "not_ipns\|not_ipfs" output.err
 '