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 
/**
 * Find the best known block, and make it the tip of the block chain
 *
 * May not be called with cs_main held. May not be called in a
 * validationinterface callback.
 */
bool ActivateBestChain(CValidationState& state, const CChainParams& chainparams, std::shared_ptr<const CBlock> pblock = std::shared_ptr<const CBlock>());
CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams);
double GuessVerificationProgress(const ChainTxData& data, const CBlockIndex* pindex);
uint64_t CalculateCurrentUsage();
/**
 *  Mark one block file as pruned.
 */
void PruneOneBlockFile(const int fileNumber) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
/**
 *  Actually unlink the specified files
 */
void UnlinkPrunedFiles(const std::set<int>& setFilesToPrune);
void FlushStateToDisk();
void PruneAndFlush();
void PruneBlockFilesManual(int nManualPruneHeight);
/** (try to) add transaction to memory pool
 * plTxnReplaced will be appended to with all transactions replaced from mempool **/
bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransactionRef &tx,
                        bool* pfMissingInputs, std::list<CTransactionRef>* plTxnReplaced,
                        bool bypass_limits, const CAmount nAbsurdFee, bool test_accept=false) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
std::string FormatStateMessage(const CValidationState &state);
ThresholdState VersionBitsTipState(const Consensus::Params& params, Consensus::DeploymentPos pos);
BIP9Stats VersionBitsTipStatistics(const Consensus::Params& params, Consensus::DeploymentPos pos);
int VersionBitsTipStateSinceHeight(const Consensus::Params& params, Consensus::DeploymentPos pos);