added RR policy

src/main/java/me/prettyprint/cassandra/connection/RoundRobinBalancingPolicy.java

@@ -0,0 +1,39 @@
+package me.prettyprint.cassandra.connection;
+
+import java.util.Collection;
+import java.util.Set;
+
+import org.cliffc.high_scale_lib.Counter;
+
+import me.prettyprint.cassandra.service.CassandraHost;
+
+public class RoundRobinBalancingPolicy implements LoadBalancingPolicy {
+
+  private final Counter counter;
+
+  public RoundRobinBalancingPolicy() {
+    counter = new Counter();
+    counter.set(0);
+  }
+
+  @Override
+  public ConcurrentHClientPool getPool(Collection<ConcurrentHClientPool> pools,
+      Set<CassandraHost> excludeHosts) {
+    ConcurrentHClientPool[] pa = pools.toArray(new ConcurrentHClientPool[pools.size()]);
+    int location = getAndIncrement(pa.length);
+    ConcurrentHClientPool pool = pa[location];
+    if ( excludeHosts != null && excludeHosts.size() > 0 ) {
+      while ( excludeHosts.contains(pool.getCassandraHost()) ) {
+        pool = pa[++location == pa.length ? 0 : location]; 
+      }
+    }
+    return pool;
+  }
+
+  private int getAndIncrement(int size) {
+    int val = (int)(counter.get() % size); 
+    counter.increment();
+    return val;
+  }
+
+}