### _Why are the changes needed?_
YARN_CONF_DIR shall be added to kyuubi server classpath as HADOOP_CONF_DIR.
### _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.apache.org/docs/latest/develop_tools/testing.html#running-tests) locally before make a pull request
Closes#2082 from SteNicholas/KYUUBI-2081.
Closes#2081
c6f76c5c [SteNicholas] [KYUUBI #2081] YARN_CONF_DIR shall be added to kyuubi server classpath as HADOOP_CONF_DIR
fee5c21f [SteNicholas] [KYUUBI #2081] YARN_CONF_DIR shall be added to kyuubi server classpath as HADOOP_CONF_DIR
Authored-by: SteNicholas <programgeek@163.com>
Signed-off-by: Kent Yao <yao@apache.org>