Bug 17358: Rename COU with COUNTRY and LAN with LANG

Bug 17358: Rename COU with COUNTRY and LAN with LANG

Some installer files use COU and LAN instead of COUNTRY and LANG.

To uniformise these AVs, it would be good to use the same code.

Note that I do not think we should update existing installations

Carefully compared code.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer  <katrin.fischer@bsz-bw.de>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit 75a900d55365dc6a8d1396b68329a0679d9dc430)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
(cherry picked from commit aa231539854fe9aa0ef75daca342c8cced0b8150)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>