[test] Shorten prefix string in test_rql_role_with_unknown_vid With Python3.7, this test fails as the error message returned by rest_publish() is: <p>an error occurred while interpreting this rql directive: ObjectNotFound('toto')</p> while we previously assumed a comma after 'toto'. Fixing this by only shortening the prefix used in out.startswith().

etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances