CircleCI: Collect JUnit test reports

This makes it easier to quickly identify which tests failed in a build.
Use in-process ZooKeeper instance for testing

Use curator's TestingServer to run an in-process ZooKeeper instance for
tests, which will hopefully perform better and be more reliable than using
a child process.
Added 'Debugging' link to TOC in testing doc
Merge pull request #279 from spotify/rohan/fix-tests

Use in-process ZooKeeper instance for testing
Merge pull request #276 from spotify/rohan/test-reports

CircleCI: Collect JUnit test reports
Add a flag per issue #278 to show only deployed jobs

-RN
Added the -y flag to `helios jobs` that will show only
deployed jobs.