Allows MutatingAdmissionWebhook admission controller by default

[bsnchan]

No description provided.

[cfdreddbot]

Hey bsnchan!

Thanks for submitting this pull request! I'm here to inform the recipients of the pull request that you and the commit authors have already signed the CLA.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/155223308

The labels on this github issue will be updated when the story is started.

[jbayer]

@bsnchan @glestaris we had also discussed SecurityContextDeny [1] which is enabled by default in new GKE 1.9.x clusters. this seems like it's worth adding, even if it's done outside of this particular PR.

[1] https://kubernetes.io/docs/admin/admission-controllers/#securitycontextdeny

[bstick12]

@jbayer The SecurityContextDeny is added at https://github.com/bsnchan/kubo-release/blob/master/jobs/kube-apiserver/templates/bin/kube_apiserver_ctl.erb#L76