add num_instances as an option to control the number of driver processes
add num_instances as an option to control the number of driver processes

iychoi/syndicate-core,iychoi/syndicate-core,syndicate-storage/syndicate-core,syndicate-storage/syndicate-core,iychoi/syndicate-core,syndicate-storage/syndicate-core,iychoi/syndicate-core,syndicate-storage/syndicate-core