Windows fixes for e2e tests (#16592)

* e2e: skip task api test when windows too old

* e2e: don't run proxy on windows

e2e/ui/input/proxy.nomad

@@ -2,6 +2,11 @@ job "nomad-proxy" {
   datacenters = ["dc1", "dc2"]
   namespace   = "proxy"
 
+  constraint {
+    attribute = "${attr.kernel.name}"
+    value     = "linux"
+  }
+
   group "proxy" {
 
     network {

e2e/workload_id/taskapi_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"strings"
 	"testing"
 
 	"github.com/hashicorp/nomad/e2e/e2eutil"
@@ -87,6 +88,22 @@ func testTaskAPIWindows(t *testing.T) {
 		t.Skip("no Windows clients")
 	}
 
+	found := false
+	for _, nodeID := range winNodes {
+		node, _, err := nomad.Nodes().Info(nodeID, nil)
+		must.NoError(t, err)
+		if name := node.Attributes["os.name"]; strings.Contains(name, "2016") {
+			t.Logf("Node %s is too old to support unix sockets: %s", nodeID, name)
+			continue
+		}
+
+		found = true
+		break
+	}
+	if !found {
+		t.Skip("no Windows clients with unix socket support")
+	}
+
 	jobID := "api-win-" + uuid.Short()
 	jobIDs := []string{jobID}
 	t.Cleanup(e2eutil.CleanupJobsAndGC(t, &jobIDs))