[BUG] ErrGroup Context Cancelation

[patrick-ogrady]

Related PR: coinbase/mesh-cli#88
Regression introduced in: #89

The context returned by errgroup.WithContext is canceled as soon as g.Wait returns. If this canceled context is passed to a handler or helper, it can have unintended consequences (some functions return immediately if the context is canceled).

Source: https://godoc.org/golang.org/x/sync/errgroup

Changes

• Add test to ensure context passed to syncer handler/helper is not canceled
• Use a separate context for ErrGroup

[coveralls]

Pull Request Test Coverage Report for Build 3315

• 12 of 12 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.09%) to 69.92%

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Totals
Change from base Build 3285:	0.09%
Covered Lines:	2178
Relevant Lines:	3115

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💛 - Coveralls