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### _Why are the changes needed?_
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Make Kyuubi jars clear.
### _How was this patch tested?_
Manual test. After this PR, the packaged dir looks like:

Closes#634 from ulysses-you/extension-dir.
Closes#634
2c5009a [ulysses-you] comment
35063ea [ulysses-you] Merge branch 'master' of https://github.com/NetEase/kyuubi into extension-dir
f2b4fff [ulysses-you] init
Authored-by: ulysses-you <ulyssesyou18@gmail.com>
Signed-off-by: Kent Yao <yao@apache.org>