have a wait to quickly test a random MPC committee

[mimoo]

It'd be nice if we could choose a threshold and a number of participant and just run a test with n MPC nodes, one in each thread

[mimoo]

and then we could use https://crates.io/crates/fail to test nodes failing sometimes! Specifically these end-to-end tests would be great to have: #18 (especially now that we have a regtest docker thingy from #17