When using a non-root user to execute sysrescue-customize with the srm building function,
you won't have the rights to create files owned by root. When you want to keep the build_into_srm
dir in a git tree, you won't be able to store the file mode there. But using a specific file
mode is important for example for /root/.ssh
The mksquashfs pseudo file allows to solve this by overriding individual file modes like this:
cat <<EOF >recipe_dir/build_into_srm/.squashfs-pseudo
/root/.ssh m 700 root root
/root/.ssh/authorized_keys m 600 root root
EOF
