Cluster: don't rewrite slaveof config directive in cluster mode.

src/config.c

@@ -1466,8 +1466,9 @@ void rewriteConfigSlaveofOption(struct rewriteConfigState *state) {
     sds line;
 
     /* If this is a master, we want all the slaveof config options
-     * in the file to be removed. */
-    if (server.masterhost == NULL) {
+     * in the file to be removed. Note that if this is a cluster instance
+     * we don't want a slaveof directive inside redis.conf. */
+    if (server.cluster_enabled || server.masterhost == NULL) {
         rewriteConfigMarkAsProcessed(state,"slaveof");
         return;
     }