prevent execution queue being blocked by zombie processes

[connectdotz]

This PR addresses 2 use cases for spawned jest processes fail to exit properly (zombie):

1. when the user cancels the manual runs, we only end the runs but do not terminate the scheduled/running jest processes.
2. when zombie processes fail to exit after the test is finished, such as caused by external issues mentioned in here

Together, this can help the queue being blocked by the zombie processes mentioned in #1124

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resolve #1124

[coveralls]

Pull Request Test Coverage Report for Build 8562206047

Details

• 84 of 84 (100.0%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.01%) to 97.997%

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Totals
Change from base Build 8474168577:	-0.01%
Covered Lines:	3983
Relevant Lines:	3990

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💛 - Coveralls