Quarkchain devnet root chain stop mining

[ping-ke]

Issue:

1. Devnet with 2 pyquarkchain nodes stop producing blocks for hour
2. No error log was found that would cause mining to stop.
   grep -i -r "Error" cluster* | grep -v jsonrpc.py | grep -v ValueError | grep -v AttributeError | grep -v web_protocol | grep -v sst | grep -v SLAVE | grep --color=always -i Error | less -R