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
{"conf_target", RPCArg::Type::NUM,  "Fallback to wallet's confirmation target", "Confirmation target (in blocks)"},
                            {"estimate_mode", RPCArg::Type::STR,  "UNSET", "The fee estimate mode, must be one of:\n"
                            "         \"UNSET\"\n"
                            "         \"ECONOMICAL\"\n"
                            "         \"CONSERVATIVE\""},
                        },
                        "options"},
                    {"bip32derivs", RPCArg::Type::BOOL,  "false", "If true, includes the BIP 32 derivation paths for public keys if we know them"},
                },
                RPCResult{
                            "{\n"
                            "  \"psbt\": \"value\",        (string)  The resulting raw transaction (base64-encoded string)\n"
                            "  \"fee\":       n,         (numeric) Fee in " + CURRENCY_UNIT + " the resulting transaction pays\n"
                            "  \"changepos\": n          (numeric) The position of the added change output, or -1\n"
                            "}\n"
                                },
                                RPCExamples{
                            "\nCreate a transaction with no inputs\n"
                            + HelpExampleCli("walletcreatefundedpsbt", "\"[{\\\"txid\\\":\\\"myid\\\",\\\"vout\\\":0}]\" \"[{\\\"data\\\":\\\"00010203\\\"}]\"")
                                },
                            }.ToString());
    RPCTypeCheck(request.params, {
        UniValue::VARR,
        UniValueType(), 
        UniValue::VNUM,
        UniValue::VOBJ,
        UniValue::VBOOL
        }, true
    );
    CAmount fee;