allow cgroupfs mounting on cgns kernels
allow cgroupfs mounting on cgns kernels

Signed-off-by: Serge Hallyn <3df611b026e4639bee8aef7a4beb2e39fcebb313@ubuntu.com>

lxc/lxd-pkg-ubuntu,lxc/lxd-pkg-ubuntu,lxc/lxd-pkg-ubuntu