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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>
 [](https://github.com/yaooqinn/kyuubi/pull/359)    [❨?❩](https://pullrequestbadge.com/?utm_medium=github&utm_source=yaooqinn&utm_campaign=badge_info)<!-- PR-BADGE: PLEASE DO NOT REMOVE THIS COMMENT -->
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the default versions may be missing if 'MVN' is absent,
```
SPARK_HOME: /Users/kentyao/kyuubi/externals/kyuubi-download/target/spark--bin-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
- [x] [Run test](https://kyuubi.readthedocs.io/en/latest/tools/testing.html#running-tests) locally before make a pull request
```
SPARK_HOME: /Users/kentyao/kyuubi/externals/kyuubi-download/target/spark-3.0.2-bin-hadoop2.7
SPARK_CONF_DIR:
HADOOP_CONF_DIR:
Candidate Kyuubi lib /Users/kentyao/kyuubi/jars doesn't exist, searching development environment...
Starting org.apache.kyuubi.server.KyuubiServer, logging to /Users/kentyao/kyuubi/logs/kyuubi-kentyao-org.apache.kyuubi.server.KyuubiServer-hulk.local.out
Welcome to
__ __ __
/\ \/\ \ /\ \ __
\ \ \/'/' __ __ __ __ __ __\ \ \____/\_\
\ \ , < /\ \/\ \/\ \/\ \/\ \/\ \\ \ '__`\/\ \
\ \ \\`\\ \ \_\ \ \ \_\ \ \ \_\ \\ \ \L\ \ \ \
\ \_\ \_\/`____ \ \____/\ \____/ \ \_,__/\ \_\
\/_/\/_/`/___/> \/___/ \/___/ \/___/ \/_/
/\___/
\/__/
```
Closes#359 from yaooqinn/356.
2014862 [Kent Yao] [KYUUBI #356] Fix missing default versions
Authored-by: Kent Yao <yao@apache.org>
Signed-off-by: Kent Yao <yao@apache.org>
