devstack behaves differently in grenade than in itself

[Radosław Piliszek]

I know the summary sounds shady but bear with me. [0]

In Ironic Grenade jobs, I discovered a peculiarity in the way that devstack config variables are handled.
The tests were on Grenade from Wallaby to current master (Xena). [1]
It turns out that the variable controlling the Cirros version was picked up fine in devstack jobs (i.e., in this case it would pass on Wallaby), yet undefined in Grenade and hence redefined entirely by Ironic's defaults.

[0] https://contenthub-static.grammarly.com/blog/wp-content/uploads/2017/02/BEAR-WITH-ME-.jpg

[1] https://review.opendev.org/c/openstack/ironic/+/786176

[Riccardo Pittau (rpittau)]

I would like to add that, looking at some old logs, we also noticed the same behavior from victoria to wallaby (during the last cycle) but they were hidden by the fact that cirros versions are the same between the 2 branches.
As a workaround, we're now reading the value of CIRROS_VERSION from stackrc, as can be seen in the patch linked by Radoslaw in the bug description.