expose `old_worker_count` in stats url
expose `old_worker_count` in stats url

This allows one to write a script that waits for the result of a
phased-restart command to complete

looker/puma,looker/puma,unleashed/puma,looker/puma,prathamesh-sonpatki/puma,respire/puma,prathamesh-sonpatki/puma,looker/puma,wallclockbuilder/puma,puma/puma,unleashed/puma,respire/puma,wallclockbuilder/puma,respire/puma,wallclockbuilder/puma,eileencodes/puma,ngpestelos/puma,puma/puma,puma/puma,respire/puma,prathamesh-sonpatki/puma,kyledrake/puma,ngpestelos/puma,ngpestelos/puma,kyledrake/puma,eileencodes/puma,eileencodes/puma,wallclockbuilder/puma,ngpestelos/puma,eileencodes/puma,unleashed/puma,puma/puma,prathamesh-sonpatki/puma,unleashed/puma,kyledrake/puma,kyledrake/puma