StorageObjectInUseProtection plugin of admission controller adds
the flag `kubernetes.io/pvc-protection` or `kubernetes.io/pv-protection`
to newly created PVCs or PV. In case a user deletes a PVC or PV the PVC
or PV is not removed until the finalizer is removed from the PVC or PV
by PVC or PV Protection Controller.
We are testing this plugin on the e2e tests of "PV Protection" because
most setup scripts enable that like:
* cluster/centos/config-default.sh: Enabled
* cluster/gce/config-default.sh: Enabled
* cluster/gce/config-test.sh: Enabled
* cluster/kubemark/gce/config-default.sh: Enabled
* hack/local-up-cluster.sh: Enabled
* cluster/juju/layers/kubernetes-master/reactive/kubernetes_master.py: Disabled
As we are testing it normally, it is nice to enable the plugin by
default.