Move the cgroup setup code out of the lxc_controller.c file
and into lxc_cgroup.{c,h}. This reduces the size of the
lxc_controller.c file and paves the way to invoke cgroup
setup from lxc_driver.c instead of lxc_controller.c in the
future
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>