* rename lxc.init_cmd to lxc.init.cmd
* rename lxc.init_uid to lxc.init.uid
* rename lxc.init_gid to lxc.init.gid

the legacy keys will be kept around until LXC 3.0 and then will be
removed.
Signed-off-by: 0x0916 <w@laoqinren.net>