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 
{
private:
    
    const uint64_t k0, k1;
public:
    SaltedTxidHasher();
    size_t operator()(const uint256& txid) const {
        return SipHashUint256(k0, k1, txid);
    }
};
/**
 * CTxMemPool stores valid-according-to-the-current-best-chain transactions
 * that may be included in the next block.
 *
 * Transactions are added when they are seen on the network (or created by the
 * local node), but not all transactions seen are added to the pool. For
 * example, the following new transactions will not be added to the mempool:
 * - a transaction which doesn't meet the minimum fee requirements.
 * - a new transaction that double-spends an input of a transaction already in
 * the pool where the new transaction does not meet the Replace-By-Fee
 * requirements as defined in BIP 125.
 * - a non-standard transaction.
 *