Sentinel: use CLIENT SETNAME when connecting to Redis.

This makes debugging / monitoring of Sentinels simpler since you can
identify sentinels in CLIENT LIST output of Redis instances.

src/sentinel.c

@@ -1615,6 +1615,23 @@ void sentinelSendAuthIfNeeded(sentinelRedisInstance *ri, redisAsyncContext *c) {
     }
 }
 
+/* Use CLIENT SETNAME to name the connection in the Redis instance as
+ * sentinel-<first_8_chars_of_runid>-<connection_type>
+ * The connection type is "cmd" or "pubsub" as specified by 'type'.
+ *
+ * This makes it possible to list all the sentinel instances connected
+ * to a Redis servewr with CLIENT LIST, grepping for a specific name format. */
+void sentinelSetClientName(sentinelRedisInstance *ri, redisAsyncContext *c, char *type) {
+    char name[64];
+
+    snprintf(name,sizeof(name),"sentinel-%.8s-%s",server.runid,type);
+    if (redisAsyncCommand(c, sentinelDiscardReplyCallback, NULL,
+        "CLIENT SETNAME %s", name) == REDIS_OK)
+    {
+        ri->pending_commands++;
+    }
+}
+
 /* Create the async connections for the specified instance if the instance
  * is disconnected. Note that the SRI_DISCONNECTED flag is set even if just
  * one of the two links (commands and pub/sub) is missing. */
@@ -1637,6 +1654,7 @@ void sentinelReconnectInstance(sentinelRedisInstance *ri) {
             redisAsyncSetDisconnectCallback(ri->cc,
                                             sentinelDisconnectCallback);
             sentinelSendAuthIfNeeded(ri,ri->cc);
+            sentinelSetClientName(ri,ri->cc,"cmd");
         }
     }
     /* Pub / Sub */
@@ -1657,6 +1675,7 @@ void sentinelReconnectInstance(sentinelRedisInstance *ri) {
             redisAsyncSetDisconnectCallback(ri->pc,
                                             sentinelDisconnectCallback);
             sentinelSendAuthIfNeeded(ri,ri->pc);
+            sentinelSetClientName(ri,ri->pc,"pubsub");
             /* Now we subscribe to the Sentinels "Hello" channel. */
             retval = redisAsyncCommand(ri->pc,
                 sentinelReceiveHelloMessages, NULL, "SUBSCRIBE %s",