fix for missing lxc-ps command in ocf:heartbeat:lxc

since beginning of 2014 the lxc-ps command isn't available anymore
(see:
https://lists.linuxcontainers.org/pipermail/lxc-devel/2014-January/007433.html)
so it is using now lxc-info to determine the PID of a container and "ps"
to get the command name of it.