Adds a failure and error tag to JUnit output so that Bamboo (and presumably other CI systems) will parse the file correctly.

We were running into an issue where Bamboo was treating each test as different from last time it was ran because it had a different (uniquely generated) class name based on the test_set. This meant that a test suite that has 3 failures would show as 3 *new* failures each time it's run rather than 3 *existing* failures.