Add err()/err_if_not_set()

* err() and err_if_not_set() do error-like reporting without aborting the script
* die_if_not_set() now properly dies
* add is_running() from Grenade

Change-Id: I38b88112415a3c07e35bbc2dc65ad839c4d63fce
Merge "Add err()/err_if_not_set()"