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 
UnlinkPrunedFiles(setFilesToPrune);
            nLastWrite = nNow;
        }
        
        if (fDoFullFlush && !pcoinsTip->GetBestBlock().IsNull()) {
            
            
            
            
            
            if (!CheckDiskSpace(GetDataDir(), 48 * 2 * 2 * pcoinsTip->GetCacheSize())) {
                return AbortNode(state, "Disk space is low!", _("Error: Disk space is low!"));
            }
            
            if (!pcoinsTip->Flush())
                return AbortNode(state, "Failed to write to coin database");
            nLastFlush = nNow;
            full_flush_completed = true;
        }
    }
    if (full_flush_completed) {
        
        GetMainSignals().ChainStateFlushed(chainActive.GetLocator());
    }
    } catch (const std::runtime_error& e) {
        return AbortNode(state, std::string("System error while flushing: ") + e.what());
    }
    return true;
}
void FlushStateToDisk() {