if there is slot migrating, proxy online should be allowed

Update config.ini

fix testcase

bugfix: WaitForReceiver didn't kill proxies correctly

Update README.md

fix migration bug

fix premigrate bug

use github.com/xiam/resp

reuse a zk connection for high frequency scene to reduce zk pressure …

…and logs

fix PRE_MIGRATE not block bug, CodisLabs#240