Fix functional jobs by installing missing dependencies
Six is needed for the OVS/OVN compilation and tox to run the tests
Update OVS/OVN to version 2.12 in order to have possibility to
compile it under Ubuntu Bionic.
There is no need to compile OVS kernel module for functional tests,
so disable it.
Signed-off-by: Lucas Alvares Gomes <email@example.com>
(cherry picked from commit b568395182)