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 (!est_fileout.IsNull())
            ::feeEstimator.Write(est_fileout);
        else
            LogPrintf("%s: Failed to write fee estimates to %s\n", __func__, est_path.string());
        fFeeEstimatesInitialized = false;
    }
    
    if (pcoinsTip != nullptr) {
        FlushStateToDisk();
    }
    
    
    GetMainSignals().FlushBackgroundCallbacks();
    
    
    
    
    
    {
        LOCK(cs_main);
        if (pcoinsTip != nullptr) {
            FlushStateToDisk();
        }
        pcoinsTip.reset();
        pcoinscatcher.reset();
        pcoinsdbview.reset();
        pblocktree.reset();
    }
    for (const auto& client : interfaces.chain_clients) {
        client->stop();