Final patch for 1.5.1 release
Okay. I turned on branch-protection rules for any *-maintenance branches. I saved the last cherry-pick for 1.5.1 to put in this PR in order to test/check that CI works right for this maintenance branch. I assume that the publishing checks and actions will work the same for releases no matter which branch they come from.
Notably - there were some conflicts I had to resolve (since this PR was originally built on some stuff that was excluded from this patch release). So @PietroPasotti and/or @pengale - if you could confirm that the xenial issues are still fixed here - that would be great.
Can we add the smoke test to the 1.5.1 branch? That would make it a lost easier to do things like verify that xenial is working. :-)
@pengale - done (I cherry-picked it into this PR).