Fix to allow to retry of failed close calls on entities#376

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yvgopal wants to merge 2 commits intoAzure:master1.0from yvgopal:close_failure_retry

+239-16

Commits on Jul 19, 2019

Fixing client entity close issues. Close failure resets the isClosing flag so close can be attempted again. Concurrent close calls shouldn't while close is still in progress
yvgopal
committed
Adding one more test case.
yvgopal
committed