[KYUUBI apache#4749] Fix flaky test issues in SchedulerPoolSuite

### _Why are the changes needed?_

To fix issue apache#4713, a PR  apache#4714 was submitted, but it had Flaky test issues. After 50 local tests, it succeeded 38 times and failed 12 times.
This PR addresses the issue of flaky tests.

### _How was this patch tested?_
- [ ] Add some test cases that check the changes thoroughly including negative and positive cases if possible

- [ ] Add screenshots for manual tests if appropriate

- [x] [Run test](https://kyuubi.readthedocs.io/en/master/develop_tools/testing.html#running-tests) locally before make a pull request

Closes apache#4749 from huangzhir/fixtest-schedulerpool.

Closes apache#4749

2d2e140 [huangzhir] call KyuubiSparkContextHelper.waitListenerBus() to make sure there are no more events in the spark event queue
52a34d2 [fwang12] [KYUUBI apache#4746] Do not recreate async request executor if has been shutdown
d4558ea [huangzhir] Merge branch 'master' into fixtest-schedulerpool
44c4cef [huangzhir] make sure the SparkListener has received the finished events for job1 and job2.
8a753e9 [huangzhir] make sure job1 started before job2
e66ede2 [huangzhir] fixbug TEST SchedulerPoolSuite  a false positive result

Lead-authored-by: huangzhir <306824224@qq.com>
Co-authored-by: fwang12 <fwang12@ebay.com>
Signed-off-by: Cheng Pan <chengpan@apache.org>

externals/kyuubi-spark-sql-engine/src/test/scala/org/apache/kyuubi/engine/spark/SchedulerPoolSuite.scala

@@ -21,6 +21,7 @@ import java.util.concurrent.Executors
 
 import scala.concurrent.duration.SECONDS
 
+import org.apache.spark.KyuubiSparkContextHelper
 import org.apache.spark.scheduler.{SparkListener, SparkListenerJobEnd, SparkListenerJobStart}
 import org.scalatest.concurrent.PatienceConfiguration.Timeout
 import org.scalatest.time.SpanSugar.convertIntToGrainOfTime
@@ -101,6 +102,8 @@ class SchedulerPoolSuite extends WithSparkSQLEngine with HiveJDBCTestHelper {
       })
       threads.shutdown()
       threads.awaitTermination(20, SECONDS)
+      // make sure the SparkListener has received the finished events for job1 and job2.
+      KyuubiSparkContextHelper.waitListenerBus(spark)
       // job1 should be started before job2
       assert(job1StartTime < job2StartTime)
       // job2 minShare is 2(total resource) so that job1 should be allocated tasks after