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
{"", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "",
                                {
                                    {"txid", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "The transaction id"},
                                    {"vout", RPCArg::Type::NUM, RPCArg::Optional::NO, "The output number"},
                                    {"scriptPubKey", RPCArg::Type::STR_HEX, RPCArg::Optional::NO, "script key"},
                                    {"redeemScript", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED, "(required for P2SH) redeem script"},
                                    {"witnessScript", RPCArg::Type::STR_HEX, RPCArg::Optional::OMITTED, "(required for P2WSH or P2SH-P2WSH) witness script"},
                                    {"amount", RPCArg::Type::AMOUNT, RPCArg::Optional::OMITTED, "(required for Segwit inputs) the amount spent"},
                                },
                                },
                        },
                        },
                    {"sighashtype", RPCArg::Type::STR,  "ALL", "The signature hash type. Must be one of:\n"
            "       \"ALL\"\n"
            "       \"NONE\"\n"
            "       \"SINGLE\"\n"
            "       \"ALL|ANYONECANPAY\"\n"
            "       \"NONE|ANYONECANPAY\"\n"
            "       \"SINGLE|ANYONECANPAY\"\n"
                    },
                },
                RPCResult{
            "{\n"
            "  \"hex\" : \"value\",                  (string) The hex-encoded raw transaction with signature(s)\n"
            "  \"complete\" : true|false,          (boolean) If the transaction has a complete set of signatures\n"
            "  \"errors\" : [                      (json array of objects) Script verification errors (if there are any)\n"
            "    {\n"
            "      \"txid\" : \"hash\",              (string) The hash of the referenced, previous transaction\n"
            "      \"vout\" : n,                   (numeric) The index of the output to spent and used as input\n"
            "      \"scriptSig\" : \"hex\",          (string) The hex-encoded signature script\n"