Avoid seatd error in guest container

Avoid seatd error in guest container

After the scarthgap update, the weson couldn't handle input device
in guest container.  It causes by libseat error that use by weston 13.
This patch add environment variable to avoid seatd error.

Bug-AGL: SPEC-5158

Change-Id: If7f88b9381e1f6af13e8f80275fda7b20ee1aa78
Signed-off-by: Naoto Yamaguchi <naoto.yamaguchi@aisin.co.jp>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl-demo/+/29968
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>