Reported here: https://github.com/bitcoin/bitcoin/pull/10244#issuecomment-378035305

Travis log here: https://travis-ci.org/bitcoin/bitcoin/jobs/361243719#L2810

Note the JSON exception:

```
test_framework.authproxy.JSONRPCException: The mempool was not loaded yet (-1) 
```

That exception was introduced here: https://github.com/bitcoin/bitcoin/commit/cb1e319fe9e198c9c5cf5236fe9af5a3d748b9e8#diff-a0c8f511d90e83aa9b5857e819ced344R1617

cc @jtimon 
WAIT_LOCK(cs_blockchange, lock);
        if(timeout)
            cond_blockchange.wait_for(lock, std::chrono::milliseconds(timeout), [&height]{return latestblock.height >= height || !IsRPCRunning();});
        else
            cond_blockchange.wait(lock, [&height]{return latestblock.height >= height || !IsRPCRunning(); });
        block = latestblock;
    }
    UniValue ret(UniValue::VOBJ);
    ret.pushKV("hash", block.hash.GetHex());
    ret.pushKV("height", block.height);
    return ret;
}
static UniValue syncwithvalidationinterfacequeue(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() > 0) {
        throw std::runtime_error(
            RPCHelpMan{"syncwithvalidationinterfacequeue",
                "\nWaits for the validation interface queue to catch up on everything that was there when we entered this function.\n",
                {},
                RPCResults{},
                RPCExamples{
                    HelpExampleCli("syncwithvalidationinterfacequeue","")
            + HelpExampleRpc("syncwithvalidationinterfacequeue","")
                },
            }.ToString());
    }
    SyncWithValidationInterfaceQueue();
    return NullUniValue;
}
static UniValue getdifficulty(const JSONRPCRequest& request)