Add cluster or sentinel to proc title

If you launch redis with `redis-server --sentinel` then
in a ps, your output only says "redis-server IP:Port" — this
patch changes the proc title to include [sentinel] or
[cluster] depending on the current server mode:
e.g.  "redis-server IP:Port [sentinel]"
      "redis-server IP:Port [cluster]"

src/redis.c

@@ -3079,10 +3079,15 @@ void redisOutOfMemoryHandler(size_t allocation_size) {
 
 void redisSetProcTitle(char *title) {
 #ifdef USE_SETPROCTITLE
-    setproctitle("%s %s:%d",
+    char *server_mode = "";
+    if (server.cluster_enabled) server_mode = " [cluster]";
+    else if (server.sentinel_mode) server_mode = " [sentinel]";
+
+    setproctitle("%s %s:%d%s",
         title,
         server.bindaddr_count ? server.bindaddr[0] : "*",
-        server.port);
+        server.port,
+        server_mode);
 #else
     REDIS_NOTUSED(title);
 #endif