creates an HTTP Raft client
retrieve current state of Raft service
add generic type to future returned by init
replica' toString is its raw URI

* The log store the replica information extracted from toString and pass it back to ClusterConfig to find a replica
move prober utility to core
explicitly initialize raft resource and do not return anything on commit

* returning Object on commit poses some serialization issues
completed integration test with only HTTP components

* tests is verbose and redundant with NettyRaftServiceTest, some stuff could be factorized especially the cluster configuration which could be made more generic