fix issue RedisLabs#94 cluster mode stuck

add missing bufferevent_disable for connections that
complete to send new requests

Author: YaacovHazan

shard_connection.cpp

@@ -465,8 +465,10 @@ void shard_connection::fill_pipeline(void)
         }
 
         // don't exceed requests
-        if (m_conns_manager->hold_pipeline(m_id))
+        if (m_conns_manager->hold_pipeline(m_id)) {
+            bufferevent_disable(m_bev, EV_WRITE|EV_READ);
             break;
+        }
 
         // client manage requests logic
         m_conns_manager->create_request(now, m_id);