[test, html validation] make validator selection somewhat smarter (at least it works properly when content is demoted from xhtml to html, making the XMLDemotingValidator class useless

if versions_map['cubicweb'][0] == (3, 7, 4):
    config['http-session-time'] *= 60
    config['cleanup-session-time'] *= 60
    config['cleanup-anonymous-session-time'] *= 60