[monorepo] Contract tests fail on second consecutive run, probably b/c of machine tests from first run

[emansipater]

Most likely this is because the machine uses truffle to build artifacts but the contracts folder uses waffle, and we were previously relying on the assumption that the build output was the same for both (when both were on truffle).

To replicate, run yarn test twice in the monorepo root.

[snario]

Potential fix: have machine make a second folder to put build artifacts in vs relying on the build folder in contracts. The reason it uses that now is because on the first run it can re-use the compile step from the contracts yarn build command instead of doing another compilation.