Work around django-storages bug by uploading XLSX
Work around django-storages bug by uploading XLSX

exports all at once, without chunking. Fixes #1556

onaio/kpi,kobotoolbox/kpi,kobotoolbox/kpi,onaio/kpi,onaio/kpi,kobotoolbox/kpi,onaio/kpi,kobotoolbox/kpi,kobotoolbox/kpi