Provide a shouldDelete hook in Qualifier interface

[jian-he]

Currently, the Qualifier has a ShouldProvision hook for external-provisioner to determine whether shouldProvision or not.

// Qualifier is an optional interface implemented by provisioners to determine
// whether a claim should be provisioned as early as possible (e.g. prior to
// leader election).
type Qualifier interface {
	// ShouldProvision returns whether provisioning for the claim should
	// be attempted.
	ShouldProvision(*v1.PersistentVolumeClaim) bool
}

Similarly, we can add a shouldDelete hook for external-provisioner to determine whether to delete the PV or not. - we implemented a custom provisioner and would like to inject logic for deletion such as time-based or space-based deletion policy.

shouldDelete(volume *v1.PersistentVolume) bool

@jsafrane , does this make sense ?

[wongma7]

yes, can be added. note that in the meantime there is also the option for Delete to return IgnoredError. The difference is that ShouldProvision/ShouldDelete gets called before Delete even gets called.

[zhangxiaoyu-zidif]

great！ we can add this method to avoid many outer processes. thumbs up.