Allow forced backup deletion

Add --force and --confirm to `ark backup delete` to support forced
backup deletion. This forcibly removes the Ark GC finalizer (if it's
present) from a backup and will orphan any resources associated with the
backup, such as backup tarballs in object storage, persistent volume
snapshots, and restores for the backup.

If a backup has a deletion timestamp, display `Deleting` in `ark backup
describe` and `ark backup get`.

Signed-off-by: Andy Goldstein <andy.goldstein@gmail.com>

pkg/controller/backup_controller.go

@@ -49,6 +49,7 @@ import (
 	"github.com/heptio/ark/pkg/util/collections"
 	"github.com/heptio/ark/pkg/util/encode"
 	kubeutil "github.com/heptio/ark/pkg/util/kube"
+	"github.com/heptio/ark/pkg/util/stringslice"
 )
 
 const backupVersion = 1
@@ -237,8 +238,8 @@ func (controller *backupController) processBackup(key string) error {
 	backup.Status.Version = backupVersion
 
 	// add GC finalizer if it's not there already
-	if !has(backup.Finalizers, gcFinalizer) {
-		backup.Finalizers = append(backup.Finalizers, gcFinalizer)
+	if !stringslice.Has(backup.Finalizers, api.GCFinalizer) {
+		backup.Finalizers = append(backup.Finalizers, api.GCFinalizer)
 	}
 
 	// calculate expiration