contrib: Clean up previous_releases.py
contrib: Clean up previous_releases.py

* Replace curl single char options with their verbose counterpart
* Stricter check for tarballHash


Former-commit-id: bdd51a10a205be4cd7417a1847526ac7f3296e2d
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin