Comment 4 for bug 1416512

Ok, so the tie-together is this:

- testr is a runner runner
- it's interface to run tests is limited to test ids
- its interface to /filter/ tests is limited to data included in test enumeration

So to fix this:
A - get subunit.run to include the attrs in enumeration in some fashion
B - teach testr to filter based on attrs as well as ids
C - stop mangling the test ids in subunit.run

-> the change here becomes just B