sim: testsuite: improve parallel test processing

The current logic limits itself to a maxdepth of 4 when looking for
results.  This wouldn't be a problem if cris didn't have a testsuite
at a depth of 5 which we end up ignoring when summarizing.  Rather
than bump the number from 4 to 5, rework the code so that we gather
the exact set of tests that we tried to run.