The kernel rejects attempts to create user namespaces when in a chroot.

Change-Id: I6548302732c8f5be52f4167cd7233aea16839ad8
Reviewed-on: https://go-review.googlesource.com/17214Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>