fix: The removeIdleTimeoutConnectionsTimer did not clean up when the … (#2384)

* fix: The removeIdleTimeoutConnectionsTimer did not clean up when the pool was closed.

* test: when the pool is closed, it should clean up timers.

Author: foxling

lib/pool.js

@@ -100,6 +100,7 @@ class Pool extends EventEmitter {
 
   end(cb) {
     this._closed = true;
+    clearTimeout(this._removeIdleTimeoutConnectionsTimer);
     if (typeof cb !== 'function') {
       cb = function(err) {
         if (err) {

test/integration/test-pool-release-idle-connection.js

@@ -38,7 +38,6 @@ pool.getConnection((err1, connection1) => {
           connection4.release();
           connection4.destroy();
           pool.end();
-          setTimeout(() => process.exit(0), 1000);
         });
       }, 7000);
     });