Add unit tests for all generators

generate_json.py does not exist any longer. Using the checks there
and move them into test_negative_generators.py. From now on the checks
are usable for all generators (also valid_generator) using a base class.

In order to check for unknown types it was mandatory to change an
existing exception to a more detailed exception (TypeError).

Partially implements bp unit-tests

Change-Id: I6b5b66f8ae113c1aca471d8338334cd47ff45723
Merge "Add unit tests for all generators"