HBASE-8778 Region assigments scan table directory making them slow for huge tables

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HBASE-9126 Make HFile MIN VERSION as 2

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HBASE-8627 HBCK can not fix meta not assigned issue

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HBASE-9129 Scanner prefetching leaks scanners.

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HBASE-9129 Scanner prefetching leaks scanners. -- MISSED DELETE

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