HPCC-8668 Roxie takes a significantly long time loading data

It would appear that we lost the use of IDelayedFile when we refactored Roxie.
On further reflection, the use of delayedFile should really be under the
control of the lazyOpen flag.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #3999 from richardkchapman/roxie-lazyopen

HPCC-8668 Roxie takes a significantly long time loading data

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>