Conditionalize error message trimming, allow node error through noLogMatcher

Trim was blowing up when an error object was passed to it. Sindre might have
noticed that this would happen earlier :sheep:.

Allow the node error message through so users and maintainers have more info on
what's happening, but still display the missing deps warning as this is the
reason for most (all?) 'spawn ENOENT' errors.
Test that we've generated the correct files

Because we've conditionalized all our tests they were passing when we didn't
generate any of the expected files. We do need to add error emitting to the
plugin.