HBASE-22929 - MemStoreLAB ChunkCreator may memory leak(ram)

[ramkrish86]

The leak is caused as said by @binlijin. The updateReaders() has already the memstoreScanners() list and so that is not getting closed.
We need to close the scanners if the close() has already happened. The test case added here helps to identify the problem. Without the patch the test fails and with patch the test passes.
@chenxu14 - Pls take a look if this will solve the problem.
@binlijin - I just realised that the memstoreScanners() were passed by the Hstore#notifyChangedReadersObservers() and not got from the updateReaders().

[binlijin]

+1

[chenxu14]

lgtm，Sir

[Apache-HBase]

🎊 +1 overall

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💚	hadoopcheck	17m 41s	Patch does not cause any errors with Hadoop 2.8.5 2.9.2 or 3.1.2.
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Subsystem	Report/Notes
Docker	Client=19.03.1 Server=19.03.1 base: https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-614/1/artifact/out/Dockerfile
GITHUB PR	#614
Optional Tests	dupname asflicense javac javadoc unit spotbugs findbugs shadedjars hadoopcheck hbaseanti checkstyle compile
uname	Linux b5419a7bb99f 4.15.0-58-generic #64-Ubuntu SMP Tue Aug 6 11:12:41 UTC 2019 x86_64 GNU/Linux
Build tool	maven
Personality	/home/jenkins/jenkins-slave/workspace/HBase-PreCommit-GitHub-PR_PR-614/out/precommit/personality/provided.sh
git revision	master / c0e5c15
Default Java	1.8.0_181
Test Results	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-614/1/testReport/
Max. process+thread count	4315 (vs. ulimit of 10000)
modules	C: hbase-server U: hbase-server
Console output	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-614/1/console
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