Test that bad Finished messages are rejected.

That's a pretty obvious thing to test. I'm not sure how we forgot that one.

Change-Id: I7e1a7df6c6abbdd587e0f7723117f50d09faa5c4
Reviewed-on: https://boringssl-review.googlesource.com/4211
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/test/runner/handshake_server.go b/ssl/test/runner/handshake_server.go
index 1ab4c5f..5db0487 100644
--- a/ssl/test/runner/handshake_server.go
+++ b/ssl/test/runner/handshake_server.go
@@ -846,6 +846,9 @@
 
 	finished := new(finishedMsg)
 	finished.verifyData = hs.finishedHash.serverSum(hs.masterSecret)
+	if c.config.Bugs.BadFinished {
+		finished.verifyData[0]++
+	}
 	c.serverVerify = append(c.serverVerify[:0], finished.verifyData...)
 	hs.finishedBytes = finished.marshal()
 	hs.writeServerHash(hs.finishedBytes)