Release 1.8.1 is a small patch release, which updates network plugins, but also tolerates a new schema
file that will be added in kops 1.9.0.  This will provide a downgrade option from kops 1.9.0.

* Ignore keyset.yaml files; provide a downgrade option from (upcoming) kops 1.9.0
* Update flannel, weave, romana, kopeio-networking, calico, canal
* Stop passing deprecated require-kubeconfig flag for kubernetes >= 1.9