ssh/test: skip tests if run as root

Fixes golang/go#14269

Change-Id: I8819de040e5f5ca3e46819d71b0cd9145b6de6d5
Reviewed-on: https://go-review.googlesource.com/109475
Reviewed-by: Han-Wen Nienhuys <hanwen@google.com>
Run-TryBot: Han-Wen Nienhuys <hanwen@google.com>

ssh/test/test_unix_test.go

@@ -302,6 +302,13 @@ func newServerForConfig(t *testing.T, config string, configVars map[string]strin
 	if testing.Short() {
 		t.Skip("skipping test due to -short")
 	}
+	u, err := user.Current()
+	if err != nil {
+		t.Fatalf("user.Current: %v", err)
+	}
+	if u.Name == "root" {
+		t.Skip("skipping test because current user is root")
+	}
 	dir, err := ioutil.TempDir("", "sshtest")
 	if err != nil {
 		t.Fatal(err)