os/user: skip tests that create users when running on dev machines

Creating and deleting users is tricky to get right, and it's not
something we want to do on a developer machine. This change skips the
tests that create users when not running on a Go builder.

This will fix #70396, although I still don't understand why the test
user couldn't be recreated.

Fixes #70396

Change-Id: Ie7004dc209f94e72152c7d6bd8ec95cc12c79757
Reviewed-on: https://go-review.googlesource.com/c/go/+/627877
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

src/os/user/user_windows_test.go

@@ -24,6 +24,13 @@ import (
 // If the user already exists, it will be deleted and recreated.
 // The caller is responsible for closing the token.
 func windowsTestAccount(t *testing.T) (syscall.Token, *User) {
+	if testenv.Builder() == "" {
+		// Adding and deleting users requires special permissions.
+		// Even if we have them, we don't want to create users on
+		// on dev machines, as they may not be cleaned up.
+		// See https://dev.go/issue/70396.
+		t.Skip("skipping non-hermetic test outside of Go builders")
+	}
 	const testUserName = "GoStdTestUser01"
 	var password [33]byte
 	rand.Read(password[:])