Add 'config' option to lxc-archlinux template and fix getopt string

This option allows user to control installation repository and options
using alternative pacman configuration file.
Also remove unnecessary sed invocation during container configuration.

Signed-off-by: Alexander Vladimirov <alexander.idkfa.vladimirov@gmail.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>
use pkg-config to ensure python3-devel is installed

The Python.h header varies in location by distribution, so instead use
pkg-config to ensure the python3 devel package is installed. Tested with
Ubuntu 12.04 and Fedora 17. Fixes --enable-python on Fedora 17.

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>