WAL: better errors and new fail point (#3246)

* privval: more info in errors

* wal: change Debug logs to Info

* wal: log and return error on corrupted wal instead of panicing

* fail: Exit right away instead of sending interupt

* consensus: FAIL before handling our own vote

allows to replicate #3089:
- run using `FAIL_TEST_INDEX=0`
- delete some bytes from the end of the WAL
- start normally

Results in logs like:

```
I[2019-02-03|18:12:58.225] Searching for height module=consensus wal=/Users/ethanbuchman/.tendermint/data/cs.wal/wal height=1 min=0 max=0
E[2019-02-03|18:12:58.225] Error on catchup replay. Proceeding to start ConsensusState anyway module=consensus err="failed to read data: EOF"
I[2019-02-03|18:12:58.225] Started node module=main nodeInfo="{ProtocolVersion:{P2P:6 Block:9 App:1} ID_:35e87e93f2e31f305b65a5517fd2102331b56002 ListenAddr:tcp://0.0.0.0:26656 Network:test-chain-J8JvJH Version:0.29.1 Channels:4020212223303800 Moniker:Ethans-MacBook-Pro.local Other:{TxIndex:on RPCAddress:tcp://0.0.0.0:26657}}"
E[2019-02-03|18:12:58.226] Couldn't connect to any seeds module=p2p
I[2019-02-03|18:12:59.229] Timed out module=consensus dur=998.568ms height=1 round=0 step=RoundStepNewHeight
I[2019-02-03|18:12:59.230] enterNewRound(1/0). Current: 1/0/RoundStepNewHeight module=consensus height=1 round=0
I[2019-02-03|18:12:59.230] enterPropose(1/0). Current: 1/0/RoundStepNewRound module=consensus height=1 round=0
I[2019-02-03|18:12:59.230] enterPropose: Our turn to propose module=consensus height=1 round=0 proposer=AD278B7767B05D7FBEB76207024C650988FA77D5 privValidator="PrivValidator{AD278B7767B05D7FBEB76207024C650988FA77D5 LH:1, LR:0, LS:2}"
E[2019-02-03|18:12:59.230] enterPropose: Error signing proposal module=consensus height=1 round=0 err="Error signing proposal: Step regression at height 1 round 0. Got 1, last step 2"
I[2019-02-03|18:13:02.233] Timed out module=consensus dur=3s height=1 round=0 step=RoundStepPropose
I[2019-02-03|18:13:02.233] enterPrevote(1/0). Current: 1/0/RoundStepPropose module=consensus
I[2019-02-03|18:13:02.233] enterPrevote: ProposalBlock is nil module=consensus height=1 round=0
E[2019-02-03|18:13:02.234] Error signing vote module=consensus height=1 round=0 vote="Vote{0:AD278B7767B0 1/00/1(Prevote) 000000000000 000000000000 @ 2019-02-04T02:13:02.233897Z}" err="Error signing vote: Conflicting data"
```

Notice the EOF, the step regression, and the conflicting data.

* wal: change errors to be DataCorruptionError

* exit on corrupt WAL

* fix log

* fix new line

consensus/state.go

@@ -307,6 +307,23 @@ func (cs *ConsensusState) OnStart() error {
 	// reload from consensus log to catchup
 	if cs.doWALCatchup {
 		if err := cs.catchupReplay(cs.Height); err != nil {
+			// don't try to recover from data corruption error
+			if IsDataCorruptionError(err) {
+				cs.Logger.Error("Encountered corrupt WAL file", "err", err.Error())
+				cs.Logger.Error("Please repair the WAL file before restarting")
+				fmt.Println(`You can attempt to repair the WAL as follows:
+
+----
+WALFILE=~/.tendermint/data/cs.wal/wal
+cp $WALFILE ${WALFILE}.bak # backup the file
+go run scripts/wal2json/main.go $WALFILE > wal.json # this will panic, but can be ignored
+rm $WALFILE # remove the corrupt file
+go run scripts/json2wal/main.go wal.json $WALFILE # rebuild the file without corruption
+----`)
+
+				return err
+			}
+
 			cs.Logger.Error("Error on catchup replay. Proceeding to start ConsensusState anyway", "err", err.Error())
 			// NOTE: if we ever do return an error here,
 			// make sure to stop the timeoutTicker
@@ -624,6 +641,15 @@ func (cs *ConsensusState) receiveRoutine(maxSteps int) {
 			cs.handleMsg(mi)
 		case mi = <-cs.internalMsgQueue:
 			cs.wal.WriteSync(mi) // NOTE: fsync
+
+			if _, ok := mi.Msg.(*VoteMessage); ok {
+				// we actually want to simulate failing during
+				// the previous WriteSync, but this isn't easy to do.
+				// Equivalent would be to fail here and manually remove
+				// some bytes from the end of the wal.
+				fail.Fail() // XXX
+			}
+
 			// handles proposals, block parts, votes
 			cs.handleMsg(mi)
 		case ti := <-cs.timeoutTicker.Chan(): // tockChan: