Improve FuzzySnapshotRelatedTest to avoid flaky due to issues like connection loss

hanm noticed that the test might failure because of ConnectionLoss when trying to getData, here is an example, we should catch this and retry to avoid flaky.

Internally, we 'fixed' flaky test by adding junit.RetryRule in ZKTestCase, which is the base class for most of the tests. I'm not sure this is the right way to go or not, since it's actually 'hiding' the flaky tests, but this will help reducing the flaky tests a lot if we're not going to tackle it in the near time, and we can check the testing history to find out which tests are flaky and deal with them separately. So let me know if this seems to provide any benefit in short term, if it is I'll provide a patch to do that.