cleanup client after disconnect

lib/sequelize/connector-manager.js

@@ -39,6 +39,7 @@ ConnectorManager.prototype.query = function(sql, callee, options) {
 
 ConnectorManager.prototype.disconnect = function() {
   this.client.end(function() {})
+  this.client = null
 }
 
 ConnectorManager.prototype.reconnect = function() {
@@ -105,4 +106,4 @@ ConnectorManager.prototype._disconnectIfNoConnections = function() {
   this.disconnectTimeoutId = setTimeout(function() {
     self.isConnected && self.hasNoConnections && self.disconnect()
   }, 100)
-}
\ No newline at end of file
+}