Sentry mock: mine block with 1 tx (#2017)

cmd/headers/download/downloader.go

cmd/headers/download/sentry_mock_test.go

cmd/integration/commands/snapshot_check.go

cmd/integration/commands/stages.go

cmd/integration/commands/state_stages.go

eth/backend.go

eth/protocols/eth/handlers.go

eth/protocols/eth/tx_pool.go

eth/stagedsync/stage_mining_create_block.go

eth/stagedsync/stage_mining_exec.go

eth/stagedsync/stage_mining_finish.go

eth/stagedsync/stagebuilder.go

eth/stagedsync/stagedsync.go

turbo/stages/stageloop.go