Comment 4 for bug 1632862

I reproduced it in a local Yakkety test bed. This seems to have something to do with the newer version of Angular in Yakkety. Looking at the JS console, I see this:

angular.js?v=2.1.0(beta3+bzr5477):6
TypeError: Converting circular structure to JSON
    at Object.toJson (http://localhost:10001/MAAS/combo/angular.js?v=2.1.0(beta3+bzr5477):2:11966)
    at RegionConnection.callMethod (http://localhost:10001/MAAS/combo/maas-angular.js?v=2.1.0(beta3+bzr5477):783:41)
    at Manager.SubnetsManager.scanSubnet (http://localhost:10001/MAAS/combo/maas-angular.js?v=2.1.0(beta3+bzr5477):2368:37)
    at Scope.$scope.actionGo (http://localhost:10001/MAAS/combo/maas-angular.js?v=2.1.0(beta3+bzr5477):16109:32)
    at fn (eval at compile (http://localhost:10001/MAAS/combo/angular.js?v=2.1.0(beta3+bzr5477):7:5437), <anonymous>:4:215)
    at expensiveCheckFn (http://localhost:10001/MAAS/combo/angular.js?v=2.1.0(beta3+bzr5477):7:29272)
    at callback (http://localhost:10001/MAAS/combo/angular.js?v=2.1.0(beta3+bzr5477):10:3936)
    at Scope.$eval (http://localhost:10001/MAAS/combo/angular.js?v=2.1.0(beta3+bzr5477):8:15047)
    at Scope.$apply (http://localhost:10001/MAAS/combo/angular.js?v=2.1.0(beta3+bzr5477):8:15395)
    at HTMLButtonElement.<anonymous> (http://localhost:10001/MAAS/combo/angular.js?v=2.1.0(beta3+bzr5477):10:4052)(anonymous function) @ angular.js?v=2.1.0(beta3+bzr5477):6

So we need to find out why we're passing the region a circular structure in Yakkety but not in Xenial.