simlib: allow to use --cores as a synonym for --procs
Ticket is here: https://bitbucket.org/einsteintoolkit/tickets/issues/1150/simfactory-it-doesnt-honor-procs-when
Ticket is here: https://bitbucket.org/einsteintoolkit/tickets/issues/1150/simfactory-it-doesnt-honor-procs-when