Cluster: make valgrind happy initializing all the bytes of the node IP.

src/cluster.c

@@ -333,7 +333,7 @@ clusterNode *createClusterNode(char *nodename, int flags) {
     node->configdigest = NULL;
     node->configdigest_ts = 0;
     node->link = NULL;
-    node->ip[0] = '\0';
+    memset(node->ip,0,sizeof(node->ip));
     node->port = 0;
     return node;
 }