Simulate network delay in tests

[penberg]

Pull request #18 fixes an issue with out-of-order or stray AppendEntries rejects, which is only trigger able when Little Raft is wired up with networked servers.

Let's improve the tests to simulate network delay and partitioning to attempt to catch bugs like these.

[penberg]

One way to do this is to use Maelstrom for testing: https://github.com/jepsen-io/maelstrom.

[andreev-io]

Help definitely wanted on this one. Do you have any tests from ChiselStore that we can reuse @penberg?

[penberg]

@andreev-io No tests to share. All the issues I discovered so far were result of manual testing and ChiselStore is still at early stages. I think first step is to improve Little Raft tests.