[BFSS] mark fs_imported value as uncachable This will finally fix the `test_bfss_fs_importing_transparency` pass again. Regression was introduced by 4ba11607d84a

#!/bin/sh -e
if [ "$1" = "purge" ] ; then
        update-rc.d cubicweb remove >/dev/null
fi
 
#DEBHELPER#
 
exit 0