Disable pep517 which doesn't work for us for now

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>

tox.ini

@@ -15,6 +15,7 @@ deps =
     ci: python-openid
     ci: python-openid-teams
     ci: python-openid-cla
+install_command = pip install --no-use-pep517 {opts} {packages}
 setenv =
     PAGURE_CONFIG={toxinidir}/tests/test_config
     PYTHONPATH={toxinidir}