Add 'stealth' checks

Perfect for easter eggs. Only outputs something if the check exits
non-'good'.

Change-Id: Ieff0973a6a120c93ed85f1819418f1f4cf85a8ba
Reviewed-on: https://gerrit.causes.com/22289
Tested-by: Aiden Scandella <aiden@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>