`make check`
`test_runner.py`
manual testing to be done:
[x] migration from existing txindex (on testnet: 2 minute block on startup)
[x] fresh txindex=1 with new code (testnet: 30 minutes background job)
[x] mainnet test (57 minutes for blocking migration on startup; 8.5 hours fresh indexing in background)
[x] test ElectrumX compatibility