Integration test from snapshot

[obycode]

The integration tests that run in epoch 3.0 take a significant amount of time just to boot to the initial state for the test. Anecdotal measurements show a test with 2 miners takes about 140s to boot to epoch 3.0, then the actual test only takes about 16s to complete. These numbers are on a powerful local machine, and are likely to be much longer on the CI runners. My theory is that we could speed this up by loading initial state, where the Bitcoin network and the Stacks network are already advanced into epoch 3.0.