We want to support copying of a PV with no storage class defined, for case of NFS -> NFS

[jwmatthews]

Related to issue in ui:
migtools/mig-ui#509

When we do a copy of PVs of NFS to NFS, a storageclass is typically not involved.

With current implementation we need to create a dummy storageclass on destination that has no-provisioner.

We want to update the implementation to support when 'no storageclass' is defined.

https://kubernetes.io/docs/concepts/storage/persistent-volumes/#class-1

PVCs don’t necessarily have to request a class. 

A PVC with its storageClassName set equal to "" is always interpreted to be requesting a PV with no class, so it can only be bound to PVs with no class (no annotation or one set equal to ""). 

A PVC with no storageClassName is not quite the same and is treated differently by the cluster depending on whether the DefaultStorageClass admission plugin is turned on.

If the admission plugin is turned on, the administrator may specify a default StorageClass. All PVCs that have no storageClassName can be bound only to PVs of that default. Specifying a default StorageClass is done by setting the annotation storageclass.kubernetes.io/is-default-class equal to “true” in a StorageClass object. If the administrator does not specify a default, the cluster responds to PVC creation as if the admission plugin were turned off. If more than one default is specified, the admission plugin forbids the creation of all PVCs.
If the admission plugin is turned off, there is no notion of a default StorageClass. All PVCs that have no storageClassName can be bound only to PVs that have no class. In this case, the PVCs that have no storageClassName are treated the same way as PVCs that have their storageClassName set to "".
Depending on installation method, a default StorageClass may be deployed to Kubernetes cluster by addon manager during installation.

When a PVC specifies a selector in addition to requesting a StorageClass, the requirements are ANDed together: only a PV of the requested class and with the requested labels may be bound to the PVC.

[sseago]

Fixed with #304