Review Request: HIVE-3481 - : Hiveserver is not closing the existing driver handle before executing the next command. It results in to file handle leaks.

[Kanna Karanam]

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https://reviews.apache.org/r/7151/
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Review request for hive.


Description
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Close the driver object if it exists before creating another driver object. 
Bunch of HiveServer & JDBC related unit tests are failing because of these file 
handle leaks.


This addresses bug HIVE-3481.
    https://issues.apache.org/jira/browse/HIVE-3481


Diffs
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  trunk/service/src/java/org/apache/hadoop/hive/service/HiveServer.java 1387251 

Diff: https://reviews.apache.org/r/7151/diff/


Testing
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Tesed on Windows as well as on Unix


Thanks,

Kanna Karanam