[tests/querier] use the new connection api (part 3/3)
Some adaptations to devtools/repotest:
* dead code removal
* remove session related code
In the tests:
* many tests actually don't check the querier but some generic rql
property -- when such a test needs several statements to complete a
commit, switch to session.new_cnx
* provide an assertRQLEqual helper
bgcolor = '#000000'
stylesheets = ['%s/cubicweb.css' % datadir_url]
logo = '%s/logo.png' % datadir_url
lazy = lazystr('%(bgcolor)s')