MDL-41410 Caching: move comment to the appropriate place.

MDL-38162 fixes the issue about testing the connection to the memcached
daemon, which means testing once the connection to the pool of servers
and not to each of the servers while being added to the pool.
It misses to move the comment to that code too.

cache/stores/memcache/lib.php

@@ -132,8 +132,8 @@ public function __construct($name, array $configuration = array()) {
         $this->connection = new Memcache;
         foreach ($this->servers as $server) {
             $this->connection->addServer($server[0], $server[1], true, $server[2]);
-            // Test the connection to this server.
         }
+        // Test the connection to the pool of servers.
         $this->isready = @$this->connection->set($this->parse_key('ping'), 'ping', MEMCACHE_COMPRESSED, 1);
     }
 

cache/stores/memcached/lib.php

@@ -141,6 +141,7 @@ public function __construct($name, array $configuration = array()) {
             }
             $this->connection->addServers($this->servers);
         }
+        // Test the connection to the pool of servers.
         $this->isready = @$this->connection->set("ping", 'ping', 1);
     }