Merge changes I880310f2,I9f437328,I552372db,I587fb203,I05f0bd94, ...

* changes:
  Do not leak AtomicLong from FollowerLogInformation
  Remove followers as an explicit field
  Hide AbstractLeader maps
  Hide internals of FollowerLogInformationImpl
  Speedup AbstractLeader.printFollowerStates()
  Improve RpcInvocationStrategy performance