add compilation option for load reporting

Link: https://github.com/GeneAssembly/biosal/issues/349
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
use more than 1 aggregator per spawner (1 aggregator for each 4 workers)

Link: https://github.com/GeneAssembly/biosal/issues/338
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>