This commit adds a check to subunit-trace to fail if the test run
doesn't actually run anything. Despite technically passing without
running anything, if you're passing a regex to testr that runs 0 tests
that is probably an error, so treat it as such. This also uncovered a
bug in the test_wrappers unit test where the test was using a bad test
regex but still passsing. Since we start enforcing it here the unit
test is also updated to use the proper regex.
Change-Id: I109a8cd6eb731e5b8daf5cc2d6a76498ddd48c6d
178cc4a605