[KYUUBI #5921] EngineRef#deregister should return the value

# 🔍 Description
## Issue References 🔗

This pull request fixes #

## Describe Your Solution 🔧

1. Let `org.apache.kyuubi.engine.EngineRef#deregister` have a return value so that you can determine whether `deregister` is successful.

2. Fix a flaky test, add `eventually`, because there is a delay in delete, causing UT to fail.
```
- deregister engine with existing host port *** FAILED ***
  Some(("localhost", 42445)) was not empty (EngineRefTests.scala:362)
```
https://github.com/apache/kyuubi/actions/runs/7320908364/job/19940635471

## Types of changes 🔖
- [x] Bugfix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)

## Test Plan 🧪

#### Behavior Without This Pull Request ⚰️
flaky test

https://github.com/apache/kyuubi/actions/runs/7320908364/job/19940635471

#### Behavior With This Pull Request 🎉
GA

#### Related Unit Tests
EngineRefTests.scala

"deregister engine with existing host port"

---

# Checklists
## 📝 Author Self Checklist

- [ ] My code follows the [style guidelines](https://kyuubi.readthedocs.io/en/master/contributing/code/style.html) of this project
- [ ] I have performed a self-review
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] This patch was not authored or co-authored using [Generative Tooling](https://www.apache.org/legal/generative-tooling.html)

## 📝 Committer Pre-Merge Checklist

- [x] Pull request title is okay.
- [x] No license issues.
- [x] Milestone correctly set?
- [x] Test coverage is ok
- [x] Assignees are selected.
- [x] Minimum number of approvals
- [x] No changes are requested

**Be nice. Be informative.**

Closes #5921 from cxzl25/engine_deregister.

Closes #5921

1384a43 [sychen] reorder and doc
c61bfbe [sychen] deregister

Authored-by: sychen <[email protected]>
Signed-off-by: Cheng Pan <[email protected]>

kyuubi-server/src/main/scala/org/apache/kyuubi/engine/EngineRef.scala

@@ -297,6 +297,7 @@ private[kyuubi] class EngineRef(
    *
    * @param discoveryClient the zookeeper client to get or create engine instance
    * @param extraEngineLog the launch engine operation log, used to inject engine log into it
+   * @return engine host and port
    */
   def getOrCreate(
       discoveryClient: DiscoveryClient,
@@ -312,19 +313,27 @@ private[kyuubi] class EngineRef(
    *
    * @param discoveryClient the zookeeper client to get or create engine instance
    * @param hostPort the existing engine host and port
+   * @return deregister result and message
    */
-  def deregister(discoveryClient: DiscoveryClient, hostPort: (String, Int)): Unit =
+  def deregister(discoveryClient: DiscoveryClient, hostPort: (String, Int)): (Boolean, String) =
     tryWithLock(discoveryClient) {
       // refer the DiscoveryClient::getServerHost implementation
       discoveryClient.getServiceNodesInfo(engineSpace, Some(1), silent = true) match {
         case Seq(sn) =>
           if ((sn.host, sn.port) == hostPort) {
-            info(s"Deleting engine node:$sn")
+            val msg = s"Deleting engine node:$sn"
+            info(msg)
             discoveryClient.delete(s"$engineSpace/${sn.nodeName}")
+            (true, msg)
           } else {
-            warn(s"Engine node:$sn is not matched with host&port[$hostPort]")
+            val msg = s"Engine node:$sn is not matched with host&port[$hostPort]"
+            warn(msg)
+            (false, msg)
           }
-        case _ => warn(s"No engine node found in $engineSpace")
+        case _ =>
+          val msg = s"No engine node found in $engineSpace"
+          warn(msg)
+          (false, msg)
       }
     }
 

kyuubi-server/src/test/scala/org/apache/kyuubi/engine/EngineRefTests.scala

@@ -22,6 +22,7 @@ import java.util.concurrent.Executors
 
 import scala.collection.JavaConverters._
 
+import org.scalatest.concurrent.PatienceConfiguration.Timeout
 import org.scalatest.time.SpanSugar.convertIntToGrainOfTime
 
 import org.apache.kyuubi.{KYUUBI_VERSION, Utils}
@@ -356,10 +357,12 @@ trait EngineRefTests extends KyuubiFunSuite {
     DiscoveryClientProvider.withDiscoveryClient(conf) { client =>
       val hp = engine.getOrCreate(client)
       assert(client.getServerHost(engine.engineSpace) == Option(hp))
-      engine.deregister(client, ("non_existing_host", 0))
+      assert(!engine.deregister(client, ("non_existing_host", 0))._1)
       assert(client.getServerHost(engine.engineSpace) == Option(hp))
-      engine.deregister(client, hp)
-      assert(client.getServerHost(engine.engineSpace).isEmpty)
+      assert(engine.deregister(client, hp)._1)
+      eventually(Timeout(10.seconds)) {
+        assert(client.getServerHost(engine.engineSpace).isEmpty)
+      }
     }
   }
 }