[KYUUBI #4494] bin/kyuubi should use exec to run Kyuubi server

### _Why are the changes needed?_

The difference between w/ and w/o `exec` in shell script

https://www.baeldung.com/linux/exec-command-in-shell-script

> When using exec, however, the command following exec replaces the current shell. This means no subshell is created and the current process is replaced with this new command.

We must do this change to make `bin/kyuubi` suitable for Cloudera Manager.

### _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 #4494 from wangmiao1002/master.

Closes #4494

ed9320447 [miaowang] Modify script run_kyuubi mode

Authored-by: miaowang <miaowang@gaojihealth.com>
Signed-off-by: Cheng Pan <chengpan@apache.org>

bin/kyuubi

@@ -155,7 +155,7 @@ function start_kyuubi() {
 
 function run_kyuubi() {
   echo "Starting $CLASS"
-  nice -n "${KYUUBI_NICENESS:-0}" ${cmd}
+  exec nice -n "${KYUUBI_NICENESS:-0}" ${cmd}
 }
 
 function stop_kyuubi() {