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
in.pushKV("bip32_derivs", keypaths);
        }
        
        if (!input.final_script_sig.empty()) {
            UniValue scriptsig(UniValue::VOBJ);
            scriptsig.pushKV("asm", ScriptToAsmStr(input.final_script_sig, true));
            scriptsig.pushKV("hex", HexStr(input.final_script_sig));
            in.pushKV("final_scriptSig", scriptsig);
        }
        if (!input.final_script_witness.IsNull()) {
            UniValue txinwitness(UniValue::VARR);
            for (const auto& item : input.final_script_witness.stack) {
                txinwitness.push_back(HexStr(item.begin(), item.end()));
            }
            in.pushKV("final_scriptwitness", txinwitness);
        }
        
        if (input.unknown.size() > 0) {
            UniValue unknowns(UniValue::VOBJ);
            for (auto entry : input.unknown) {
                unknowns.pushKV(HexStr(entry.first), HexStr(entry.second));
            }
            in.pushKV("unknown", unknowns);
        }
        inputs.push_back(in);
    }
    result.pushKV("inputs", inputs);
    
    CAmount output_value = 0;
    UniValue outputs(UniValue::VARR);