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
LOCK(pwallet->cs_wallet);
    UniValue obj(UniValue::VOBJ);
    size_t kpExternalSize = pwallet->KeypoolCountExternalKeys();
    const auto bal = pwallet->GetBalance();
    obj.pushKV("walletname", pwallet->GetName());
    obj.pushKV("walletversion", pwallet->GetVersion());
    obj.pushKV("balance", ValueFromAmount(bal.m_mine_trusted));
    obj.pushKV("unconfirmed_balance", ValueFromAmount(bal.m_mine_untrusted_pending));
    obj.pushKV("immature_balance", ValueFromAmount(bal.m_mine_immature));
    obj.pushKV("txcount",       (int)pwallet->mapWallet.size());
    obj.pushKV("keypoololdest", pwallet->GetOldestKeyPoolTime());
    obj.pushKV("keypoolsize", (int64_t)kpExternalSize);
    CKeyID seed_id = pwallet->GetHDChain().seed_id;
    if (pwallet->CanSupportFeature(FEATURE_HD_SPLIT)) {
        obj.pushKV("keypoolsize_hd_internal",   (int64_t)(pwallet->GetKeyPoolSize() - kpExternalSize));
    }
    if (pwallet->IsCrypted()) {
        obj.pushKV("unlocked_until", pwallet->nRelockTime);
    }
    obj.pushKV("paytxfee", ValueFromAmount(pwallet->m_pay_tx_fee.GetFeePerK()));
    if (!seed_id.IsNull()) {
        obj.pushKV("hdseedid", seed_id.GetHex());
    }
    obj.pushKV("private_keys_enabled", !pwallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS));
    return obj;
}
static UniValue listwalletdir(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() != 0) {
        throw std::runtime_error(