As mentioned in gomods#1743 the Go modules environment flag is set to `off`
in the script which appears to cause a warning message for each module
of the codebase that it is "not in GOROOT".

Set to `auto` as this allows the same build to be run the original way
should someone choose to delete the `go.mod` file from the project root.

Go 1.17 ignores `GO111MODULE` and there are no directories in the
project root called `mock`.

`golint` is deprecated (and frozen) replace with the current `go vet`.
This reported one issue on `main` branch:
```pkg/stash/with_etcd.go:33:28:
loop variable ep captured by func literal```

Fixed loop variable capture with extraction to parameterised anonymous
function passed loop variable and passed in to `errgroup.Go` call.