Comment 9 for bug 1806239

Granted, I'm using a devstack created today:

stack@stein:~/devstack$ git log -1
commit 8fc227f63fd0820bd9c5725a6023529c742d2041
Merge: 2697e43 5a9e32a
Author: Zuul <email address hidden>
Date: Wed Dec 12 23:29:07 2018 +0000

    Merge "Update comment about nova-cells-v1 job"
stack@stein:~/devstack$

So maybe I need to try and recreate this from a stable/rocky devstack, but note that in stable/rocky devstack would still install a newer python-glanceclient than you're using because it uses upper-constraints:

https://github.com/openstack/requirements/blob/stable/rocky/upper-constraints.txt#L102