test: remove errgroup to take advantage of vet

go vet would have prevented the bug fixed in
6362e32161295fa959ebe46b93cea0ea1a9bdd72 but our use of errgroup
prevented that.

Rip out errgroup to take advantage of vet, and remove download limiting
now that we're downloading far fewer binaries overall.

e2e/vault/vault_test.go

@@ -3,7 +3,6 @@ package vault
 import (
 	"archive/zip"
 	"bytes"
-	"context"
 	"encoding/json"
 	"flag"
 	"fmt"
@@ -24,7 +23,6 @@ import (
 	"github.com/hashicorp/nomad/testutil"
 	vapi "github.com/hashicorp/vault/api"
 	"github.com/stretchr/testify/require"
-	"golang.org/x/sync/errgroup"
 )
 
 var (
@@ -51,27 +49,24 @@ func syncVault(t *testing.T) ([]*version.Version, map[string]string) {
 	// Create the directory for the binaries
 	require.NoError(t, createBinDir(binDir))
 
-	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Minute)
-	defer cancel()
-
-	// Limit to N concurrent downloads
-	sema := make(chan int, 5)
-
 	// Download in parallel
 	start := time.Now()
-	g, _ := errgroup.WithContext(ctx)
+	errCh := make(chan error, len(missing))
 	for ver, url := range missing {
 		dst := filepath.Join(binDir, ver)
 		url := url
-		g.Go(func() error {
-			sema <- 1
-			defer func() {
-				<-sema
-			}()
-			return getVault(dst, url)
-		})
+		go func() {
+			errCh <- getVault(dst, url)
+		}()
+	}
+	for i := 0; i < len(missing); i++ {
+		select {
+		case err := <-errCh:
+			require.NoError(t, err)
+		case <-time.After(5 * time.Minute):
+			t.Fatalf("timed out downloading Vault binaries")
+		}
 	}
-	require.NoError(t, g.Wait())
 	if n := len(missing); n > 0 {
 		t.Logf("Downloaded %d versions of Vault in %s", n, time.Now().Sub(start))
 	}