fix(launcher): task promises run parallel

[yadimon]

fix for #5145 + cosmetics

@IgorMinar don't know yet how to write tests for this. If you let me know the way, i could add them.

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[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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[yadimon]

@googlebot I signed it!

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CLAs look good, thanks!

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[yadimon]

added some kind of unit tests for this case, i hope its acceptable