Use common get_instance call in API plugins part 2

Cleanup API to use common get_instance call which
automatically does exception handling. These changes
are in a separate patch because they required some
unittest changes because of the manner in which some
methods were originally stubbed out.

Change-Id: Ide92ba84cc937191d25da0d643e8e4427a9aa8c7
Merge "Use common get_instance call in API plugins part 2"