c/r: use criu's "full" mode for cgroups

c/r: use criu's "full" mode for cgroups

A while ago cgroup modes were introduced to CRIU, which slightly changed
the behavior w.r.t. cgroups under the hood. What we're really after is
criu's --full mode, i.e. even if a particular cgroup directory exists
(in particular /lxc/$container[-$number] will, since we create it), we
should restore perms on that cgroup.

Things worked just fine for actual properties (except "special" properties
as criu refers to them, which I've just sent a patch for) because liblxc
creates no subdirectories, just the TLD.

Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>