Add a script to run 'go vet'

@filbranden 
No worries. In that case, please add a comment stating that's your intent I guess :-)

And please use a temporary variable for the unfiltered output, test the return code to set the failed variable and last print the output piping it to grep. (You might need a `|| :` after the grep -v since it exits 1 if the resulting output is empty.)

I still recommend joining the for into a single go vet call setting the targets to "..." when not specified and using the `/#/./` trick to insert the `./` prefix to all of them, I think that would simplify this a lot.

Cheers,
Filipe