The -E flag for sudo has previously been removed to work around some
strange issues.
Re-add the safer --preserve-envs flag listing all the settings currently
available.

This allows in particular to override the serdes configuration again
without editing the runme.sh file - e.g.:
docker run -i -t -v "$PWD":/work -e SERDES=8S_9_2 lx2160a_build -u 0 -g 0
Signed-off-by: Josua Mayer <josua@solid-run.com>