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 
throw std::runtime_error(
            RPCHelpMan{"getrawmempool",
                "\nReturns all transaction ids in memory pool as a json array of string transaction ids.\n"
                "\nHint: use getmempoolentry to fetch a specific transaction from the mempool.\n",
                {
                    {"verbose", RPCArg::Type::BOOL,  "false", "True for a json object, false for array of transaction ids"},
                },
                RPCResult{"for verbose = false",
            "[                     (json array of string)\n"
            "  \"transactionid\"     (string) The transaction id\n"
            "  ,...\n"
            "]\n"
            "\nResult: (for verbose = true):\n"
            "{                           (json object)\n"
            "  \"transactionid\" : {       (json object)\n"
            + EntryDescriptionString()
            + "  }, ...\n"
            "}\n"
                },
                RPCExamples{
                    HelpExampleCli("getrawmempool", "true")
            + HelpExampleRpc("getrawmempool", "true")
                },
            }.ToString());
    bool fVerbose = false;
    if (!request.params[0].isNull())
        fVerbose = request.params[0].get_bool();
    return MempoolToJSON(::mempool, fVerbose);
}
static UniValue getmempoolancestors(const JSONRPCRequest& request)