More tests: DynamicHoneyBadger

[afck]

The DynamicHoneyBadger tests currently don't include adversaries that send messages. They should be extended in the same way as the HoneyBadger tests: #401
Or should they? What's the best way to avoid duplicating the same kind of tests for all three *HoneyBadgers? At least the adversaries' strategies here should probably focus on validator set changes (voting, key generation, etc.).

Let's also rename the file to dynamic_honey_badger.rs.

Apart from #386, are there any additional patterns of validator set changes that we should add?