HPCC-11070 Roxie returning incorrect value for thorlib.node()

Roxie returns 1 for thorlib.node() but hthor returns 0, and thor returns
0-based values.

For consistency with hthor and a 1-way thor, Roxie should be returning 0.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #5574 from richardkchapman/roxie-node

HPCC-11070 Roxie returning incorrect value for thorlib.node()

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>