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
throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed %s", error));
    }
    bool extract = request.params[1].isNull() || (!request.params[1].isNull() && request.params[1].get_bool());
    CMutableTransaction mtx;
    bool complete = FinalizeAndExtractPSBT(psbtx, mtx);
    UniValue result(UniValue::VOBJ);
    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
    std::string result_str;
    if (complete && extract) {
        ssTx << mtx;
        result_str = HexStr(ssTx.str());
        result.pushKV("hex", result_str);
    } else {
        ssTx << psbtx;
        result_str = EncodeBase64(ssTx.str());
        result.pushKV("psbt", result_str);
    }
    result.pushKV("complete", complete);
    return result;
}
UniValue createpsbt(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() < 2 || request.params.size() > 4)
        throw std::runtime_error(
            RPCHelpMan{"createpsbt",
                "\nCreates a transaction in the Partially Signed Transaction format.\n"
                "Implements the Creator role.\n",
                {
                    {"inputs", RPCArg::Type::ARR, RPCArg::Optional::NO, "A json array of json objects",
                        {