Make test_runner.py throw an error if test with parameter does not exist

Summary:
This will warn the user breaking the test_runner.py script if a file
deletion or renaming occurs.

Test Plan:
Run test_runner.py on any script, check there is no error
Modify the test_runner.py script to include a typo in any file name from
the TEST_PARAMS array, run it and check the error is detected.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2439