Backport the new ipc implementation in HBASE-16432 to branch-1

Two problems.

First, as RpcCliemtImpl is the default implementation on branch-1, we need to confirm that the modification on master does not make it slower. I'm not sure but I used a big lock to protect everything in the new implementation, so it may have bad impact on performance.

Second, some configurations of the old AsyncRpcClient is gone. Such as "hbase.rpc.client.threads.max" and "hbase.rpc.client.nativetransport". Now You could pass a EventLoopGroup object directly through a helper class which makes it more flexible.