Add Guava Service wrapper around LeaderSelector recipe.
Update LeaderService to allow the delegate service to stop itself.
Fix race condition of mutex acquisition followed immediately by zk cxn loss.
Refactor Guava LeaderService to use LeaderLatch to simplify control flow.
LeaderService code read comments.
Documentation tweaks.
Fix failed test case.
Merge pull request #18 from bazaarvoice/ssmith-leaderservice

Add Guava Service wrapper around LeaderSelector recipe.