proxy: return JSON errors
proxy: add a todo for logging
Merge pull request #1685 from xiang90/proxy

proxy: return JSON errors
integration: rewrite the way to check cluster make progress
integration: newMember -> mustNewMember
Merge pull request #1682 from yichengq/217

integration: rewrite the way to check cluster make progress
raftpb: fix proto
Merge pull request #1686 from xiang90/proto

raftpb: fix proto
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  raftpb: fix proto
  integration: newMember -> mustNewMember
  integration: rewrite the way to check cluster make progress
  proxy: add a todo for logging
  proxy: return JSON errors