HPCC-7896 Roxie CRoxiePackageSetManager holds lock for too long

This meant that during a reload (which might take a little time in some cases)
query requetss would be blocked.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #4277 from richardkchapman/roxie-reload-lock

HPCC-7896 Roxie CRoxiePackageSetManager holds lock for too long

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>