CI integration in filecoin-project/lotus

[raulk]

Once we have #221 and #222, we should set up a Circle CI job in filecoin-project/lotus that does the following:

1. Does a shallow clone of the filecoin/vm-tests repo.
   • Lock in a concrete tag/branch/commit in a .vmtests.toml config file at the root of the repo.
   • This has many benefits:
     • Explicitly declares which version of the corpus this VM implementation complies with.
     • Future-proof: allows us to conduct change management / evolution cleanly without incurring in false, noisy breakage. Removes volatility.
2. Exercises the Lotus VM against the test vectors using the test driver.
3. Populate a JUnit XML file via gotestsum so CircleCI can populate the Tests tab.

[raulk]

This is in review on lotus side: filecoin-project/lotus#3081