Add HdfsChaosMonkeyNothingIsSafeTest test.

So far I only have added a an HdfsChaosMonkeySafeLeaderTest - I figured it's the same logic as the standard FS and so just one of the two Chaos tests was good enough coverage. The other HdfsChaos test has proven very valuable in finding fails I can't as easily find with the local FS though, so it makes sense to add this class to help with testing.