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 
}
#if ENABLE_ZMQ
    if (g_zmq_notification_interface) {
        UnregisterValidationInterface(g_zmq_notification_interface);
        delete g_zmq_notification_interface;
        g_zmq_notification_interface = nullptr;
    }
#endif
    try {
        if (!fs::remove(GetPidFile())) {
            LogPrintf("%s: Unable to remove PID file: File does not exist\n", __func__);
        }
    } catch (const fs::filesystem_error& e) {
        LogPrintf("%s: Unable to remove PID file: %s\n", __func__, fsbridge::get_filesystem_error_message(e));
    }
    interfaces.chain_clients.clear();
    UnregisterAllValidationInterfaces();
    GetMainSignals().UnregisterBackgroundSignalScheduler();
    GetMainSignals().UnregisterWithMempoolSignals(mempool);
    globalVerifyHandle.reset();
    ECC_Stop();
    LogPrintf("%s: done\n", __func__);
}
/**
 * Signal handlers are very limited in what they are allowed to do.
 * The execution context the handler is invoked in is not guaranteed,
 * so we restrict handler operations to just touching variables:
 */
#ifndef WIN32
static void HandleSIGTERM(int)