Fix runner.go session ticket support.

Some test code to insert a bogus session ticket was retained. Also,
decryptTicket mutated its input, in turn, mutating the ClientHello,
breaking the Finished hash.

The latter fix should probably be merged upstream.

Change-Id: I6949f842c67e19df8742561fb0b849af9f5f099d
Reviewed-on: https://boringssl-review.googlesource.com/1290
Reviewed-by: Adam Langley <agl@google.com>

ssl/test/runner/handshake_server.go

@@ -588,10 +588,6 @@ func (hs *serverHandshakeState) sendSessionTicket() error {
 	if err != nil {
 		return err
 	}
-	m.ticket = make([]byte, 16105+62)
-	for i := range m.ticket {
-		m.ticket[i] = 'A'
-	}
 
 	hs.finishedHash.Write(m.marshal())
 	c.writeRecord(recordTypeHandshake, m.marshal())

ssl/test/runner/ticket.go

@@ -173,7 +173,7 @@ func (c *Conn) decryptTicket(encrypted []byte) (*sessionState, bool) {
 		return nil, false
 	}
 	ciphertext := encrypted[aes.BlockSize : len(encrypted)-sha256.Size]
-	plaintext := ciphertext
+	plaintext := make([]byte, len(ciphertext))
 	cipher.NewCTR(block, iv).XORKeyStream(plaintext, ciphertext)
 
 	state := new(sessionState)