Fixes/detect missing filters

The core of this pull request is the 3rd rev; 110d4e2, which adds awareness at the template level of missing filters and allows that error to propagate upwards.  In other words, the following now properly fails:


- hosts: all
  tasks:
  - debug: msg="this should fail {{ ansible_inventory_hostname|missing_filter }}"

The other two revs (dcb7722 and 146e243) fix the underlying test code this uses so they actually are working as intended (ie, undefined variables being an error is being turned on/off).

I will say, I'm not hugely happy w/ the form of the fix here, but until there is better unification of the multiple template functions in the utils.template module, this is kind of the best that comes to mind.