private String getNextRemoteDatacenter()  {
    int i = 0;
    int remoteDatacenterCount = remoteDatacenters.size();
    String nextDatacenter;
    do {
      nextDatacenter = remoteDatacenters.get(currentDatacenterIndex);
      currentDatacenterIndex = (currentDatacenterIndex + 1) % remoteDatacenterCount;
      i++;
    } while (replicaPoolByDc.get(nextDatacenter).isEmpty() &&
        i <= remoteDatacenterCount);                           // Guard against infinite loop
    return nextDatacenter;
  }
Returns the "next" remote data center that we should pick up a replica from, for insertion into the remoteReplicas
list. Remote data center names are returned in a round-robin fashion.
@return the String name of the next colo.
ambry-router/src/main/java/com/github/ambry/router/ParanoidDurabilityOperationTracker.java