grml-live: strip xattrs in squashfs

Ignore all extended attributes from files in chroot when adding them to the
squashfs.

This avoids:

1) leaking containerization supplied selinux attributes into the squashfs,
which can be seen when building in podman, and in docker.

2) prevents unpacking errors in a later build-only step in containers not
supporting xattrs. Can also be seen in podman.

On a normal machine and also on a normal (booted) Grml system, the only things
having xattrs are:

file: var/log/journal
system.posix_acl_access
system.posix_acl_default

file: var/log/journal/1e77092b16004314a93d779757d513ac
system.posix_acl_access
system.posix_acl_default

Both of these are apparently applied by systemd/journald during boot, even if
the filesystem does not have them.

grml-live

@@ -1514,6 +1514,11 @@ else
      fi
    fi
 
+   # Ignore all extended attributes. This avoids:
+   # 1) leaking containerization supplied selinux attributes into the squashfs,
+   # 2) prevents unpacking errors in a later build-only step in containers not supporting xattrs.
+   SQUASHFS_OPTIONS="$SQUASHFS_OPTIONS -no-xattrs"
+
    # support exclusion of files via exclude-file:
    if [ -n "$SQUASHFS_EXCLUDES_FILE" ] && [ "$SQUASHFS_EXCLUDES_FILE" ] ; then
       SQUASHFS_OPTIONS="$SQUASHFS_OPTIONS -ef $SQUASHFS_EXCLUDES_FILE -wildcards"