[VOL-1866] Changed module dependency to v12.0.0 of k8s client-go and v1.15.4 of k8s api/apimachinery in sync with other voltha components

Had to use pseudo-version corresponding to v12.0.0 of k8s client-go
because golang proxy is no longer serving the modules not complying
to Semantic Import Versioning rules including client-go v12.0.0.
Refer to https://github.com/kubernetes/client-go/issues/631 and
https://github.com/golang/go/issues/33558

Change-Id: I2e558bab7f0702f230761319eb5392a7d0532ea3
diff --git a/vendor/k8s.io/api/storage/v1alpha1/generated.proto b/vendor/k8s.io/api/storage/v1alpha1/generated.proto
index fdc4ad2..57a8357 100644
--- a/vendor/k8s.io/api/storage/v1alpha1/generated.proto
+++ b/vendor/k8s.io/api/storage/v1alpha1/generated.proto
@@ -21,6 +21,7 @@
 
 package k8s.io.api.storage.v1alpha1;
 
+import "k8s.io/api/core/v1/generated.proto";
 import "k8s.io/apimachinery/pkg/apis/meta/v1/generated.proto";
 import "k8s.io/apimachinery/pkg/runtime/generated.proto";
 import "k8s.io/apimachinery/pkg/runtime/schema/generated.proto";
@@ -68,6 +69,15 @@
   // Name of the persistent volume to attach.
   // +optional
   optional string persistentVolumeName = 1;
+
+  // inlineVolumeSpec contains all the information necessary to attach
+  // a persistent volume defined by a pod's inline VolumeSource. This field
+  // is populated only for the CSIMigration feature. It contains
+  // translated fields from a pod's inline VolumeSource to a
+  // PersistentVolumeSpec. This field is alpha-level and is only
+  // honored by servers that enabled the CSIMigration feature.
+  // +optional
+  optional k8s.io.api.core.v1.PersistentVolumeSpec inlineVolumeSpec = 2;
 }
 
 // VolumeAttachmentSpec is the specification of a VolumeAttachment request.