ISPN-4409 Upgrade to LevelDB 0.7 and fix server test assertions

* Upgrade to LevelDB 0.7 in order to align with server's Guava
version which currently is 16.x.
* Fixed LevelDB server test assertions to avoid having to instantiate
the cache's marshaller client side.
ISPN-4012 Mark mass indexing tests as unstable
ISPN-4414 Compatible failover request load balancer for HR clients
ISPN-4414 Update documentation to use new request balancing interface