This patch fixes multiple issues to unblock gate:
1. With new isort releases (5.X.X) pylint started to fail, with error:
AttributeError: module 'isort' has no attribute 'SortImports'
This patch pin isort to 4.3.21, the last version before 5.0.0.
2. lower-constraints of appdirs and pytz need to be updated as
currently lower-constraints job fails.
Since patch Ia012a8e116a276a6674f86366c803e0e2d8ff704 modified the
NEUTRON_PATH variable the functional test fails with:
[..]neutron/tools/configure_for_func_testing.sh: line 113: /home/zuul/src/opendev.org/openstack/neutron-vpnaas/devstack/lib/ovs: No such file or directory
3. Functional job fails, because during tox run the latest released
neutron is installed and it requires mock to be installed. This
patch adds mock to functional test requirements. Note: this needs
to be deleted as soon as new neutron will be released as on
development branch neutron does not depend on mock anymore.
Change-Id: Ibc4cd7f8a055457b288ef101893c252cf0464a28
2b293a1bfa