Revisit the logic for updating Cassandra nodes

[gmaretic]

Following up on PDS-94960, where we ended up unable to talk to Cassandra.

Since the updates happen only every 2 minutes, trying to talk to a single node that is not blacklisted, it is possible that we got unlucky and ended up in a state where all the old nodes were decommissioned before we were able to find out about any of the new ones.

[jeremyk-91]

This is fishy:

    private List<TokenRange> getTokenRanges() throws Exception {
        return getRandomGoodHost().runWithPooledResource(CassandraUtils.getDescribeRing(config));
    }