Update the list of expected "id" outputs in
TestGroupCleanupUserNamespace with SELinux context information as used
on CentOS.

Fixes #34547

Change-Id: I426bbe2d04e2039c87490362a1891ec3de6e36e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/197841
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>