Gerrit 3.8 has been released for a bit. Update our 3.8 image builds to
pull the latest 3.8.1 version for testing.
Gerrit 3.7.4 has also been released. We update our 3.7 images to 3.7.4.
Note this is our production image and this update will affect prod
unlike the 3.8.0 update. Changelog is here:
https://www.gerritcodereview.com/3.7.html#374
The only breaking change is related to prometheus metrics which we
aren't using (yet).
Change-Id: I52854ed097e295c070e642808e9dae793dc8a716