Prevent user introspection of Python objects

The get_attr and get_param built-in functions in HOT allowed introspection
of Python objects as well as traversing lists and maps, which we very much
do not want.

Fixes bug #1280526

Change-Id: I5f8f4bfa37d33eb0a1df962b69a3b6e029ad0048
Merge "Prevent user introspection of Python objects"