Move cassandra fixtures to the pytest plugin
So other packages (eg. swh-scrubber) can use them in their own tests.
Imports are not at the toplevel, so this doesn't add a hard dependency on cassandra-driver.
Staging instance, all changes can be removed at any time
So other packages (eg. swh-scrubber) can use them in their own tests.
Imports are not at the toplevel, so this doesn't add a hard dependency on cassandra-driver.