For all templates except lxc-ubuntu-cloud and lxc-download, detect not
only --mapped-uid but also --mapped-gid and error out.  Detecting will
not be done after -- parameter because of non-option parameters.

Also, change the mode of lxc-archlinux.in 100755 to 100644.
Signed-off-by: TAMUKI Shoichi <tamuki@linet.gr.jp>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>