`validate_options` needs to be extended with
`topology` parameter, because NetworkTopologyStrategy needs to validate if every
explicitly listed DC is really existing. I did cut corner a bit and
trimmed the message thrown when it's not the case, just to avoid passing
and extra parameter (ks name) to the `validate_options`
function, as I find the longer message to be a bit redundant (the driver will
receive info which KS modification failed).
The tests that have been commented out in the previous commit have been
restored.
2953d3ebe0