fix: calling block.genesis() locks default db
fix: calling block.genesis() locks default db

gsalgado/pyethapp,danielnovy/test,ethereum/pyethapp,gsalgado/pyethapp,heikoheiko/pyethapp,kustomzone/pyethapp,RomanZacharia/pyethapp,changwu-tw/pyethapp,d-das/pyethapp,ethereum/pyethapp,RomanZacharia/pyethapp,changwu-tw/pyethapp,vaporry/pyethapp