// wantedMacVersionNext returns the macOS 10.x version to create next,                                                                                               
// or 0 to not make anything. It gets the latest reverse buildlet                                                                                                    
// status from the coordinator.                                                                                                                                      
func wantedMacVersionNext(st *State, rstat *types.ReverseBuilderStatus) int {
        // TODO: improve this logic now that the coordinator has a                                                                                                   
        // proper scheduler. Instead, don't create anything                                                                                                          
        // proactively until there's demand from it from the                                                                                                         
        // scheduler. (will need to add that to the coordinator's                                                                                                    
        // status JSON) And maybe add a streaming endpoint to the                                                                                                    
        // coordinator so we don't need to poll every N seconds. Or                                                                                                  
        // just poll every few seconds, perhaps at a lighter endpoint                                                                                                
        // that only does darwin.                                                                                                                                    
        //                                                                                                                                                           
        // For now just use the static configuration in                                                                                                              
        // dashboard/builders.go of how many are expected, which ends                                                                                                
        // up in ReverseBuilderStatus.