Fixing problem caused by activerecord

ActiveRecord installed a parent() method that seems to have wreaked
havoc on the inheritance traversing code in the variable lookup code.
This uses a new method that achieves the same end, but doesn't rely as
much on the duck typing (responds to :parent) of the resource.

In addition tests have been added for node inheritance to ensure that
that inheritance heirarchy is followed as we expect. Also tests that
tried to fake out things and now have incorrect assumptions have been
changed to make fewer assumptions about how the system works.