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 
{
                    {"action", RPCArg::Type::STR, RPCArg::Optional::NO, "The action to execute\n"
            "                                      \"start\" for starting a scan\n"
            "                                      \"abort\" for aborting the current scan (returns true when abort was successful)\n"
            "                                      \"status\" for progress report (in %) of the current scan"},
                    {"scanobjects", RPCArg::Type::ARR, RPCArg::Optional::NO, "Array of scan objects\n"
            "                                  Every scan object is either a string descriptor or an object:",
                        {
                            {"descriptor", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "An output descriptor"},
                            {"", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "An object with output descriptor and metadata",
                                {
                                    {"desc", RPCArg::Type::STR, RPCArg::Optional::NO, "An output descriptor"},
                                    {"range", RPCArg::Type::RANGE,  "1000", "The range of HD chain indexes to explore (either end or [begin,end])"},
                                },
                            },
                        },
                        "[scanobjects,...]"},
                },
                RPCResult{
            "{\n"
            "  \"unspents\": [\n"
            "    {\n"
            "    \"txid\" : \"transactionid\",     (string) The transaction id\n"
            "    \"vout\": n,                    (numeric) the vout value\n"
            "    \"scriptPubKey\" : \"script\",    (string) the script key\n"
            "    \"desc\" : \"descriptor\",        (string) A specialized descriptor for the matched scriptPubKey\n"
            "    \"amount\" : x.xxx,             (numeric) The total amount in " + CURRENCY_UNIT + " of the unspent output\n"
            "    \"height\" : n,                 (numeric) Height of the unspent transaction output\n"
            "   }\n"
            "   ,...], \n"