This is an attempt to fix the flaky consensus/ethash tests under macOS.
* consensus, miner: stale block supporting * consensus, miner: refactor seal signature * cmd, consensus, eth: add miner noverify flag * cmd, consensus, miner: polish
* miner: commit state which is relative with sealing result * consensus, core, miner, mobile: introduce sealHash interface * miner: evict pending task with threshold * miner: go fmt