* rename lxc.logfile to lxc.log.file
* renaem lxc.loglevel to lxc.log.level
* rename lxc.syslog to lxc.log.syslog

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