Previously, if there was an error such as a broken .t file that caused
run-tests.py to encounter an exception during parsing, the test would be
considered in an "errored" state, which is separate from "failed".
The check for whether to exit non-zero or not was based entirely on whether
there were any tests in a "failed" state, so if there was only an error,
run-tests would exit with 0. Our test infrastructure would then consider the
test as passing, causing us to have some tests with false negatives that have
gone undetected for a few weeks now.