travis run: https://travis-ci.org/bitcoin/bitcoin/jobs/406813397

```
rpc_psbt.py failed, Duration: 4 s
stdout:
2018-07-22T13:28:57.765000Z TestFramework (INFO): Initializing test directory /tmp/bitcoin_test_runner_20180722_132530/rpc_psbt_49
2018-07-22T13:29:00.531000Z TestFramework (ERROR): Assertion failed
Traceback (most recent call last):
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/test_framework/test_framework.py", line 160, in main
    self.run_test()
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/rpc_psbt.py", line 101, in run_test
    assert_raises_rpc_error(-22, "TX decode failed", self.nodes[0].converttopsbt, signedtx['hex'])
  File "/home/travis/build/bitcoin/bitcoin/build/bitcoin-x86_64-unknown-linux-gnu/test/functional/test_framework/util.py", line 105, in assert_raises_rpc_error
    assert try_rpc(code, message, fun, *args, **kwds), "No exception raised"
AssertionError: No exception raised
{
    std::shared_ptr<CWallet> const wallet = GetWalletForJSONRPCRequest(request);
    CWallet* const pwallet = wallet.get();
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() < 2 || request.params.size() > 4) {
        std::string msg =
            RPCHelpMan{"addmultisigaddress",
                "\nAdd a nrequired-to-sign multisignature address to the wallet. Requires a new wallet backup.\n"
                "Each key is a Bitcoin address or hex-encoded public key.\n"
                "This functionality is only intended for use with non-watchonly addresses.\n"
                "See `importaddress` for watchonly p2sh address support.\n"
                "If 'label' is specified, assign address to that label.\n",
                {
                    {"nrequired", RPCArg::Type::NUM, RPCArg::Optional::NO, "The number of required signatures out of the n keys or addresses."},
                    {"keys", RPCArg::Type::ARR, RPCArg::Optional::NO, "A json array of bitcoin addresses or hex-encoded public keys",
                        {
                            {"key", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "bitcoin address or hex-encoded public key"},
                        },
                        },
                    {"label", RPCArg::Type::STR, RPCArg::Optional::OMITTED_NAMED_ARG, "A label to assign the addresses to."},
                    {"address_type", RPCArg::Type::STR,  "set by -addresstype", "The address type to use. Options are \"legacy\", \"p2sh-segwit\", and \"bech32\"."},
                },
                RPCResult{
            "{\n"
            "  \"address\":\"multisigaddress\",    (string) The value of the new multisig address.\n"
            "  \"redeemScript\":\"script\"         (string) The string value of the hex-encoded redemption script.\n"