HPCC-9795 Roxie needs to figure out numChannels

Some hidden attributes that were calcluated by configmgr were not in the xsd,
or were marked as readonly there. configmgr no longer calculates them, making
it very hard to set up a new Roxie cluuster.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4706 from richardkchapman/roxie-config-cockup

HPCC-9795 Roxie needs to figure out numChannels

Reviewed By Gavin
Tested by Chris