do not send whole round state via eventHub

Fixes

```
WARNING: DATA RACE
Write at 0x00c4200715b8 by goroutine 24:
  github.com/tendermint/tendermint/consensus.(*ConsensusState).enterPrevote.func1()
      /go/src/github.com/tendermint/tendermint/consensus/state.go:359 +0x3f
  github.com/tendermint/tendermint/consensus.(*ConsensusState).enterPrevote()
      /go/src/github.com/tendermint/tendermint/consensus/state.go:897 +0x8de
  github.com/tendermint/tendermint/consensus.(*ConsensusState).addProposalBlockPart()
      /go/src/github.com/tendermint/tendermint/consensus/state.go:1303 +0x701
  github.com/tendermint/tendermint/consensus.(*ConsensusState).handleMsg()
      /go/src/github.com/tendermint/tendermint/consensus/state.go:560 +0x88c
  github.com/tendermint/tendermint/consensus.(*ConsensusState).receiveRoutine()
      /go/src/github.com/tendermint/tendermint/consensus/state.go:525 +0x6d2

Previous read at 0x00c4200715b8 by goroutine 19:
  github.com/tendermint/tendermint/consensus.makeRoundStepMessages()
      /go/src/github.com/tendermint/tendermint/consensus/reactor.go:415 +0x192
  github.com/tendermint/tendermint/consensus.(*ConsensusReactor).broadcastNewRoundStep()
      /go/src/github.com/tendermint/tendermint/consensus/reactor.go:377 +0x3c
  github.com/tendermint/tendermint/consensus.(*ConsensusReactor).broadcastNewRoundStepsAndVotes.func1()
      /go/src/github.com/tendermint/tendermint/consensus/reactor.go:350 +0x275
```

consensus/types/state.go

@@ -77,10 +77,20 @@ type RoundState struct {
 // RoundStateEvent returns the H/R/S of the RoundState as an event.
 func (rs *RoundState) RoundStateEvent() types.EventDataRoundState {
 	edrs := types.EventDataRoundState{
-		Height:     rs.Height,
-		Round:      rs.Round,
-		Step:       rs.Step.String(),
-		RoundState: rs,
+		Height: rs.Height,
+		Round:  rs.Round,
+		Step:   rs.Step.String(),
+		// send only fields needed by makeRoundStepMessages
+		RoundState: &RoundState{
+			Height:             rs.Height,
+			Round:              rs.Round,
+			Step:               rs.Step,
+			StartTime:          rs.StartTime,
+			LastCommit:         rs.LastCommit,
+			LockedBlock:        rs.LockedBlock,   // consensus/state_test.go#L398
+			ProposalBlock:      rs.ProposalBlock, // consensus/state_test.go#L253
+			ProposalBlockParts: rs.ProposalBlockParts,
+		},
 	}
 	return edrs
 }