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/executor/util/util.go

@@ -57,7 +57,7 @@ func WaitTimeout(wg *sync.WaitGroup, timeout time.Duration) {
 }
 
 // ConvertConfigSecrets returns envFromSource which can be passed directly into the pod spec
-func ConvertConfigSecrets(ctx context.Context, fn *fv1.Function, kc *kubernetes.Clientset) ([]apiv1.EnvFromSource, error) {
+func ConvertConfigSecrets(ctx context.Context, fn *fv1.Function, kc kubernetes.Interface) ([]apiv1.EnvFromSource, error) {
 
 	cmList := fn.Spec.ConfigMaps
 	secList := fn.Spec.Secrets