Opening /proc/<pid>/pagemap in userns is only available since linux
v4.3 or later, after commit 1c90308e7a77 (pagemap: hide physical
addresses from non-privileged users). So those tests fail on older
kernels:
https://ci.openvz.org/job/CRIU/job/CRIU-virtuozzo/job/criu-dev/1402

travis-ci: success for zdtm: do not run cow0x tests in userns
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>