If a default storage class exists, it is going to create a new persistent volume to bind to that claim instead of using our example one, which will make the tutorial fail. In particular, this happens on minikube.
Specifying an empty storageClassName will prevent the storage class to be used, and force our volume to be selected.
* update pod persistent volume example storage class
When binding to a manually created PersistentVolume, the claim must
disable dynamic provisioning by specifying an empty storage class.
Fixes#2803
* use specific storageclass
* revert gibibytes -> gigabytes change