Appveyor smoke tests are flaky

[patrickhulce]

Appveyor only passes the byte-efficiency smoke tests ~80% of the time (2 of last 10 builds on master have failed, and anecdotally it feels like lots of my PRs get red status checks).

It's going to be difficult to get consistent results on appveyor since we discovered how crazy variable their CPU performance is, we might want to loosen our expectations on smokehouse just in appveyor/run multiple times/adjust estimate if we detect very slow CPU/etc.