[FIX] web: avoid expensive 404 during js tests

A 404 will take 3 to 5 seconds to be resolved and execute +- 1900 query, to return
a rendered page which is quite expensive, especially when multiple missing images
are rendered in a view.

Catching static route and marking them as not frontend will help to avoid to handle miss
on static resources. In this case server returns a standard 404.

This commit also fix a iframe src in order to avoid a 404 on
/web/(test )/report/html/some_report (thx to aab-odoo)