Add a script to run 'go vet'

@filbranden 
With `set -o pipefail` we'll start failing if any command fails.  That is probably what you want.  You can probably get rid of the grep.

I'd try:
```
trap 'exit 1' SIGINT

failures=0
for arg; do
  go vet "${goflags[@]:0}" ./... 2>&1 || {
    failures=$((failures + 1))
  }
done
exit $failures
```