Testing liquidation value

[Schwartz10]

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[Schwartz10]

@jimpick it would be super helpful if you could take this one across the finish line, there are a few things left to tackle:

1. We should run this test on say 10 miners in parallel rather than just 1 miner. I couldn't get the precise method to play nicely in parallel with the various channels and inside the test runner.
2. We should make sure that each miner that gets tested has active sectors (rather than just the one we're choosing)
3. We should double check the accuracy of the AssertApproxEqRel func (i wrote tests, but it would be nice to get more confidence)