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.

This works with lxc version 1.0.0.alpha3 and newer (2013-11-15).
The command and output formatting were added/changed in commit 5444216b7ee04a65679d9999d3933450bf817536