Code review comment for lp:~gz/bzr/use_testtools_timings_625594

There's a run that vila launched on babune with this change and the testtools change with a subset of the tests:
<http://babune.ladeuil.net:24842/view/debug/job/selftest-subset-all/93/aggregatedTestReport/>

Has some interesting things you can drill down to from the grouped timings, for instance, of the 10 seconds it takes to run bt.test_workingtree_4 on gentoo:
<http://babune.ladeuil.net:24842/job/selftest-subset-gentoo/75/testReport/bzrlib.tests.test_workingtree_4/TestWorkingTreeFormat4/>
There are 4 seconds each in test_commit_updates_hash_cache and test_observed_sha1_cachable (they sleep).

Also useful for comparing the different platforms on the same suite or test.