Allow just a single test to be run

Our run_tests.py presently has a '--test' argument that lets you only run just a single test module, or all test modules with a given prefix.

This is nice, but often we want to only run a single test. For example, just test/integ/control/controller.py's test_reattaching_listeners() method.

Presently you could test only this module with...

% ./run_tests.py --integ --test control.controller

But better would be to let you drill down even more like...

% ./run_tests.py --integ --test control.controller.test_reattaching_listeners