buildbot-effects steps run even if flake build fails

[antifuchs]

I would expect the effects to be skipped if any of the build steps fail, but that is apparently not so: This build had a build step (a prereq to one of the effects run, in fact) fail and the effects got run anyway.

[Mic92]

#399 was trying to address but somehow it didn't fully work?

[antifuchs]

Hm, I don't think I was running with that yet. I can try running with it in a few days.