issue #661: Refine a path resolution for node tasks

[rzymek01]

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Summary

• an executable (such as gulp) is found regardless of extension used (supported by node, i.e. no extension, js, json, and node)
• revamp log messages
• reuse paths-related utils

Tests and Documentation

I've tested the change locally in a few scenarios with different correct/invalid task paths.

I can see gulp happy path is already covered in it/example project. I'm wondering why it didn't fail for 1.6 release... Should I add new directory in it especially for this change? IMO docs change it's not needed here, because it's about internal behaviour, but I might be wrong.

[rzymek01]

@eirslett bumping