test: speed up parallel/test-tls-session-cache

This test had some unnecessary timeouts that made it run for a
much longer time than necessary (about 9 s rather than 0.2 s).

PR-URL: nodejs#18424
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

test/parallel/test-tls-session-cache.js

@@ -69,11 +69,11 @@ function doTest(testOptions, callback) {
   server.on('newSession', function(id, data, cb) {
     ++newSessionCount;
     // Emulate asynchronous store
-    setTimeout(function() {
+    setImmediate(() => {
       assert.ok(!session);
       session = { id, data };
       cb();
-    }, 1000);
+    });
   });
   server.on('resumeSession', function(id, callback) {
     ++resumeCount;
@@ -89,9 +89,9 @@ function doTest(testOptions, callback) {
     }
 
     // Just to check that async really works there
-    setTimeout(function() {
+    setImmediate(() => {
       callback(null, data);
-    }, 100);
+    });
   });
 
   server.listen(0, function() {
@@ -132,7 +132,7 @@ function doTest(testOptions, callback) {
         }
         assert.strictEqual(code, 0);
         server.close(common.mustCall(function() {
-          setTimeout(callback, 100);
+          setImmediate(callback);
         }));
       }));
     }