TT#45709 Disable Secure Boot support when building Grml ISO

The Secure Boot enabled GRUB from Ubuntu breaks EFI boot on
Dell servers (e.g. on PowerEdge R330). Until we know how
to solve this disable Secure Boot support within our ISOs.

Change-Id: I3cf96ca40b6e66c591b60b73e77ac164fd79f472

grml_build/Dockerfile

@@ -29,7 +29,7 @@ RUN apt-get update && apt-get install --assume-yes \
   syslinux \
   xorriso
 
-RUN echo "./grml-live -s buster -a amd64 -c GRMLBASE,SIPWISE,AMD64 -t /code/grml-live/templates/ -o /grml/ -r grml-sipwise -v 0.42" >/root/.bash_history
+RUN echo "SECURE_BOOT=disable ./grml-live -s buster -a amd64 -c GRMLBASE,SIPWISE,AMD64 -t /code/grml-live/templates/ -o /grml/ -r grml-sipwise -v 0.42" >/root/.bash_history
 RUN echo "export LIVE_CONF=/code/grml-live/etc/grml/grml-live.conf" >>/root/.bash_history
 RUN echo "export SCRIPTS_DIRECTORY=/code/grml-live/scripts"         >>/root/.bash_history
 RUN echo "export GRML_FAI_CONFIG=/code/grml-live/etc/grml/fai"      >>/root/.bash_history