lxc_config: Add -h and --help flags handler
lxc_config: Add -h and --help flags handler

As the other tools already handle, show usage message when -h or --help
are used.

Signed-off-by: Marcos Paulo de Souza <0b4ebe3a213a49a2bc3457b98408e6d86812eb46@gmail.com>

caglar10ur/lxc,ss1h2a3tw/lxc,thmo/lxc,ss1h2a3tw/lxc,hallyn/lxc,hallyn/lxc,thmo/lxc,thmo/lxc,caglar10ur/lxc,hallyn/lxc,caglar10ur/lxc,ss1h2a3tw/lxc