HPCC-11572 Use new child node subscription mechanism in Roxie

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6029 from richardkchapman/roxie-superfile-subscribe

HPCC-11572 Use new child node subscription mechanism in Roxie

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>