HPCC-11627 Requesting per-query logging can cause roxie cores

Appending logging information from slaves to the context was not threadsafe.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6028 from richardkchapman/roxie-logging-core

HPCC-11627 Requesting per-query logging can cause roxie cores

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>