mempool_persist.py failing in travis #12863
Description
Reported here: #10244 (comment)
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: cb1e319#diff-a0c8f511d90e83aa9b5857e819ced344R1617
cc @jtimon