[KYUUBI #4462] Fix variable usage issue in SessionManager#stop

### _Why are the changes needed?_

Fix variable usage issue in `SessionManager#stop`

### _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

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

Closes #4462 from Yikf/sessionmanager.

Closes #4462

d4340d4ec [Yikf] fix variable usage issue

Authored-by: Yikf <yikaifei@apache.org>
Signed-off-by: Cheng Pan <chengpan@apache.org>

kyuubi-common/src/main/scala/org/apache/kyuubi/session/SessionManager.scala

@@ -288,9 +288,9 @@ abstract class SessionManager(name: String) extends CompositeService(name) {
     shutdown = true
     val shutdownTimeout: Long =
       if (isServer) {
-        conf.get(ENGINE_EXEC_POOL_SHUTDOWN_TIMEOUT)
-      } else {
         conf.get(SERVER_EXEC_POOL_SHUTDOWN_TIMEOUT)
+      } else {
+        conf.get(ENGINE_EXEC_POOL_SHUTDOWN_TIMEOUT)
       }
 
     ThreadUtils.shutdown(timeoutChecker, Duration(shutdownTimeout, TimeUnit.MILLISECONDS))