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 (tip_height) {
            start_block = locked_chain->getBlockHash(start_height);
            
            
            
            
            
            if (stop_height) {
                stop_block = locked_chain->getBlockHash(*stop_height);
            }
        }
    }
    CWallet::ScanResult result =
        pwallet->ScanForWalletTransactions(start_block, stop_block, reserver, true );
    switch (result.status) {
    case CWallet::ScanResult::SUCCESS:
        break;
    case CWallet::ScanResult::FAILURE:
        throw JSONRPCError(RPC_MISC_ERROR, "Rescan failed. Potentially corrupted data files.");
    case CWallet::ScanResult::USER_ABORT:
        throw JSONRPCError(RPC_MISC_ERROR, "Rescan aborted.");
        
    }
    UniValue response(UniValue::VOBJ);
    response.pushKV("start_height", start_height);
    response.pushKV("stop_height", result.last_scanned_height ? *result.last_scanned_height : UniValue());
    return response;
}
class DescribeWalletAddressVisitor : public boost::static_visitor<UniValue>