Print verbose results if one or more tests failed within a group

http://testing.drupal.org/pifr/file/1/drupal_imageapi_373613_2.patch is the latest example of a test that fails on the testing bot server but passes locally. The only information we know is that "somewhere" in the 96 assertions within the "Image manipulation tests" group, a test failed. Without more information, this is impossible to debug.

I would love to see the full assertion output for any test groups that failed.