Replace control when control host is down or removed

Akshay Mankar requested to merge axeman/cql-io:control-conn into develop

Without doing this a graceful loss of connection with the control host is ignored and if the whole cluster is to be restarted after that, cql-io does not get any more events. When the last node in the cluster is restarted, cql-io gets into an unrecoverable state where it thinks the control host is connected, but also thinks that no hosts are reachable.

The CI is failing due to, hopefully it will get fixed soon.

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