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
{
    if (request.fHelp || request.params.size() < 1 || request.params.size() > 3) {
        throw std::runtime_error(
            RPCHelpMan{"createwallet",
                "\nCreates and loads a new wallet.\n",
                {
                    {"wallet_name", RPCArg::Type::STR, RPCArg::Optional::NO, "The name for the new wallet. If this is a path, the wallet will be created at the path location."},
                    {"disable_private_keys", RPCArg::Type::BOOL,  "false", "Disable the possibility of private keys (only watchonlys are possible in this mode)."},
                    {"blank", RPCArg::Type::BOOL,  "false", "Create a blank wallet. A blank wallet has no keys or HD seed. One can be set using sethdseed."},
                },
                RPCResult{
            "{\n"
            "  \"name\" :    <wallet_name>,        (string) The wallet name if created successfully. If the wallet was created using a full path, the wallet_name will be the full path.\n"
            "  \"warning\" : <warning>,            (string) Warning message if wallet was not loaded cleanly.\n"
            "}\n"
                },
                RPCExamples{
                    HelpExampleCli("createwallet", "\"testwallet\"")
            + HelpExampleRpc("createwallet", "\"testwallet\"")
                },
            }.ToString());
    }
    std::string error;
    std::string warning;
    uint64_t flags = 0;
    if (!request.params[1].isNull() && request.params[1].get_bool()) {
        flags |= WALLET_FLAG_DISABLE_PRIVATE_KEYS;
    }
    if (!request.params[2].isNull() && request.params[2].get_bool()) {