The bundle disco-stein was in the dev bundles because
a bug with the Python 3.7 syntax prevented the success of
the deployment of HA clusters. This bug is fixed, we can
reintegrate disco-stein in the gate bundles.
Other small additions:
- removing sitepackages in tox.ini to avoid test env pollution
- skip_missing_interpreters in tox.ini set to False to avoid false
positives by skipping missing interpreters.
Ensure that EOL releases are removed from metadata
and tests, and that the current dev release is enabled
in metadata. Dev release tests are enabled separately
because of chickens and eggs.