Use Clientset interface instead of type for Fission/kubernetes clients (#2416)

Using interface makes it easy to create a fake client and unit test
a specific portion of the code. We should be able to more write unit
test and increase coverage of code with this change.

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>

pkg/storagesvc/archivePruner.go

@@ -24,11 +24,12 @@ import (
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
 	"github.com/fission/fission/pkg/crd"
+	"github.com/fission/fission/pkg/generated/clientset/versioned"
 )
 
 type ArchivePruner struct {
 	logger        *zap.Logger
-	crdClient     *crd.FissionClient
+	crdClient     versioned.Interface
 	archiveChan   chan string
 	stowClient    *StowClient
 	pruneInterval time.Duration