management jobs schedule list query

the management jobs should only show the schedules which haven't run yet. updating the query to reflect this.

awx/ui/client/src/management-jobs/schedule/schedule.controller.js

@@ -48,7 +48,7 @@ export default [
                     scope: $scope,
                     list: SchedulesList,
                     id: 'management_jobs_schedule',
-                    url: url,
+                    url: url  + '?next_run__isnull=false',
                     pageSize: 20
                 });
             });