HPCC-9582 New feature: evaluate(module, attribute)

Will make writing unit tests much simpler and cleaner if we have a form of
evaluate(module) that only evaluates attributes matching a supplied name.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4570 from richardkchapman/evaluate-attr

HPCC-9582 New feature: evaluate(module, attribute)

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>