Issue #285, Fix rate-limiting with cluster-mode (#286)

When a connection disconnected, the timer event was not
free, and cause the test to keep running forever.

One of these cases is when we are starting the benchmark in
cluster-mode and using the replica's ip/port.

shard_connection.cpp

@@ -129,7 +129,7 @@ verify_request::~verify_request(void)
 shard_connection::shard_connection(unsigned int id, connections_manager* conns_man, benchmark_config* config,
                                    struct event_base* event_base, abstract_protocol* abs_protocol) :
         m_address(NULL), m_port(NULL), m_unix_sockaddr(NULL),
-        m_bev(NULL), m_request_per_cur_interval(0), m_pending_resp(0), m_connection_state(conn_disconnected),
+        m_bev(NULL), m_event_timer(NULL), m_request_per_cur_interval(0), m_pending_resp(0), m_connection_state(conn_disconnected),
         m_hello(setup_done), m_authentication(setup_done), m_db_selection(setup_done), m_cluster_slots(setup_done) {
     m_id = id;
     m_conns_manager = conns_man;
@@ -174,6 +174,11 @@ shard_connection::~shard_connection() {
         m_bev = NULL;
     }
 
+    if (m_event_timer != NULL) {
+        event_free(m_event_timer);
+        m_event_timer = NULL;
+    }
+
     if (m_protocol != NULL) {
         delete m_protocol;
         m_protocol = NULL;
@@ -298,8 +303,13 @@ int shard_connection::connect(struct connect_info* addr) {
 void shard_connection::disconnect() {
     if (m_bev) {
         bufferevent_free(m_bev);
+        m_bev = NULL;
+    }
+
+    if (m_event_timer != NULL) {
+        event_free(m_event_timer);
+        m_event_timer = NULL;
     }
-    m_bev = NULL;
 
     // empty pipeline
     while (m_pending_resp)