Replace golint with go vet– #1743 (#1744)

* Set GO111MODULE to auto in golint script– #1743

As mentioned in #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.

* Remove redundant code – golint script

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

* Replace `golint` with `go vet`

`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.

Makefile

@@ -47,7 +47,7 @@ setup-dev-env:
 .PHONY: verify
 verify: ## verify athens codebase
 	./scripts/check_gofmt.sh
-	./scripts/check_golint.sh
+	./scripts/check_govet.sh
 	./scripts/check_deps.sh
 	./scripts/check_conflicts.sh
 

pkg/stash/with_etcd.go

@@ -29,10 +29,13 @@ func WithEtcd(endpoints []string, checker storage.Checker) (Wrapper, error) {
 	}
 	var eg errgroup.Group
 	for _, ep := range endpoints {
-		eg.Go(func() error {
+		epStat := func(ep string) func() error {
+			return func() error {
 				_, err := c.Status(ctx, ep)
 				return err
-		})
+			}
+		}(ep)
+		eg.Go(epStat)
 	}
 	err = eg.Wait()
 	if err != nil {

scripts/check_govet.sh

@@ -4,4 +4,4 @@
 # Run the linter on everything except generated code
 set -euo pipefail
 
-golint -set_exit_status $(GO111MODULE=off go list ./... | grep -v '/mocks')
+go vet ./...