BE-494 - need to be able to refresh hosts setting for datacenter (and rack, though
    not really using it at the moment). Need this for our own dca aware round robin
which is managed by comparing the datacenter names. We can drop all of this once we
get a real dac aware option from the datastax client. The issue being addressed
here is that sometimes the datacenter and rack were coming up with their default
values "unset", which could make all of the hosts look remote. Now we can detect
this "unknown" case and refresh the hosts if needed. Note that it is difficult to
see if this is safe to do during execution. Seems like it should be since
cql_control_connection is responding to hosts being added and dropped from the cluster.