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### _Why are the changes needed?_
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When start the server, If not specified `SPARK_CONF_DIR`, it should output default.
```
KYUUBI_WORK_DIR_ROOT: /root/tmp/kyuubi/work
SPARK_HOME: /root/package/spark-3.1.2-bin-hadoop2.7
SPARK_CONF_DIR:
HADOOP_CONF_DIR: /root/package/hadoop-3.2.0/etc/hadoop
```
### _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/latest/tools/testing.html#running-tests) locally before make a pull request
Closes#896 from timothy65535/ky-895.
Closes#895
9a936a77 [timothy65535] [KYUUBI #895] Enhance output uses the default spark conf
Authored-by: timothy65535 <timothy65535@163.com>
Signed-off-by: ulysses-you <ulyssesyou18@gmail.com>
1a76d77b6f