tests: Skip tests if required tools are not available

There is no reason to fail a test if the required testing tool is not
present on the system, so skip the test instead of failing it.

Signed-off-by: Leo Sandoval <lsandova@redhat.com>
Reviewed-by: Andrew Hamilton <adhamilt@gmail.com>
Reviewed-by: Neal Gompa <ngompa13@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

tests/f2fs_test.in

@@ -12,7 +12,7 @@ fi
 
 if ! which mkfs.f2fs >/dev/null 2>&1; then
  echo "mkfs.f2fs not installed; cannot test f2fs."
- exit 99
+ exit 77
 fi