Fix get_test_run_by_run_id() db api method

The get_test_run_by_run_id() method was broken, it was using the
incorrect db model name. (a copy and paste error) so the method
would not work. This corrects the issue so you can get all the
test runs for a give run_id field.

Change-Id: I289b04f8a1a26a34be2e22507c95a80c9347b1ad