Adding more unit tests for ES v6 client

[neil-xie]

What changed?
Add unit tests for Scrolll, ClearScroll and IsNotFoundErr method

Why?
Increase test coverage

How did you test it?
Unit test

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 018e15dd-b491-421c-8766-6b4cdb3af0f9

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 85 unchanged lines in 21 files lost coverage.
• Overall coverage decreased (-0.03%) to 63.731%

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Files with Coverage Reduction	New Missed Lines	%
service/matching/matcher.go	1	91.07%
common/peerprovider/ringpopprovider/config.go	2	81.58%
common/persistence/executionManager.go	2	78.59%
common/persistence/historyManager.go	2	66.67%
common/persistence/sql/sqlplugin/mysql/db.go	2	79.49%
common/persistence/sql/sqlplugin/mysql/task.go	2	73.68%
common/task/fifo_task_scheduler.go	2	85.57%
common/task/weighted_round_robin_task_scheduler.go	2	88.56%
common/util.go	2	91.69%
service/matching/db.go	2	73.23%

Totals
Change from base Build 018e15cf-3d6d-468c-b814-72a9a96fede3:	-0.03%
Covered Lines:	93429
Relevant Lines:	146599

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💛 - Coveralls