[test] don't leave NULL columns around when making an attribute required It doesn't matter on sqlite (it doesn't do ALTER COLUMN), but when running this test on postgresql it fails to add the 'NOT NULL' constraint otherwise.

bgcolor = '#000000'
stylesheets = ['%s/cubicweb.css' % datadir_url]
logo = '%s/logo.png' % datadir_url
lazy = lazystr('%(bgcolor)s')