[QA] Zuul upgrade on April 8th

[Antoine Musso]

Hello,

I will upgrade Zuul on Monday April 8th around 7am UTC. That is merely a
maintenance upgrade with patches for long awaited fixes and will no more
block upgrading Gerrit to 2.16.

The task is https://phabricator.wikimedia.org/T208426 and list all the
bug fixes.


The most annoying bug fix is querying a change would sometime yield an
unrelated patchset which caused CI to always fail :/
https://phabricator.wikimedia.org/T198968


Thank you Paladox for all the bug you caught and the preliminary testing!

-- 
Antoine Musso