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 
*    previously active chain, all the missing transactions will have been
     *    re-added to the mempool and should be present if they meet size and
     *    consistency constraints.
     *
     * 2. Locking `mempool.cs` without `cs_main` will give a view of a mempool
     *    consistent with some chain that was active since `cs_main` was last
     *    locked, and that is fully populated as described above. It is ok for
     *    code that only needs to query or remove transactions from the mempool
     *    to lock just `mempool.cs` without `cs_main`.
     *
     * To provide these guarantees, it is necessary to lock both `cs_main` and
     * `mempool.cs` whenever adding transactions to the mempool and whenever
     * changing the chain tip. It's necessary to keep both mutexes locked until
     * the mempool is consistent with the new chain tip and fully populated.
     *
     * @par Consistency bug
     *
     * The second guarantee above is not currently enforced, but
     * https://github.com/bitcoin/bitcoin/pull/14193 will fix it. No known code
     * in bitcoin currently depends on second guarantee, but it is important to
     * fix for third party code that needs be able to frequently poll the
     * mempool without locking `cs_main` and without encountering missing
     * transactions during reorgs.
     */
    mutable RecursiveMutex cs;
    indexed_transaction_set mapTx GUARDED_BY(cs);
    using txiter = indexed_transaction_set::nth_index<0>::type::const_iterator;
    std::vector<std::pair<uint256, txiter> > vTxHashes; 
    struct CompareIteratorByHash {
        bool operator()(const txiter &a, const txiter &b) const {