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
#include <merkleblock.h>
#include <node/psbt.h>
#include <node/transaction.h>
#include <policy/policy.h>
#include <policy/rbf.h>
#include <policy/settings.h>
#include <primitives/transaction.h>
#include <psbt.h>
#include <rpc/rawtransaction_util.h>
#include <rpc/server.h>
#include <rpc/util.h>
#include <script/script.h>
#include <script/script_error.h>
#include <script/sign.h>
#include <script/standard.h>
#include <uint256.h>
#include <util/bip32.h>
#include <util/moneystr.h>
#include <util/strencodings.h>
#include <validation.h>
#include <validationinterface.h>
#include <numeric>
#include <stdint.h>
#include <univalue.h>
/** High fee for sendrawtransaction and testmempoolaccept.
 * By default, transaction with a fee higher than this will be rejected by the
 * RPCs. This can be overriden with the maxfeerate argument.
 */
constexpr static CAmount DEFAULT_MAX_RAW_TX_FEE{COIN / 10};
static void TxToJSON(const CTransaction& tx, const uint256 hashBlock, UniValue& entry)