This patch makes lxc to detect a specific cgroup dedicated to lxc
which is mounted with the lxc name. That allows to mount different
cgroup in different places with different options (aka subsystems)
and assign one to be used by lxc. If no such mount point is found,
the first cgroup mount point is used.
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>