[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/scheduling/v1alpha1/generated.proto b/vendor/k8s.io/api/scheduling/v1alpha1/generated.proto
index 5fb5472..584a291 100644
--- a/vendor/k8s.io/api/scheduling/v1alpha1/generated.proto
+++ b/vendor/k8s.io/api/scheduling/v1alpha1/generated.proto
@@ -21,6 +21,7 @@
 
 package k8s.io.api.scheduling.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";
@@ -28,6 +29,7 @@
 // Package-wide variables from generator "generated".
 option go_package = "v1alpha1";
 
+// DEPRECATED - This group version of PriorityClass is deprecated by scheduling.k8s.io/v1/PriorityClass.
 // PriorityClass defines mapping from a priority class name to the priority
 // integer value. The value can be any valid integer.
 message PriorityClass {
@@ -52,6 +54,13 @@
   // when this priority class should be used.
   // +optional
   optional string description = 4;
+
+  // PreemptionPolicy is the Policy for preempting pods with lower priority.
+  // One of Never, PreemptLowerPriority.
+  // Defaults to PreemptLowerPriority if unset.
+  // This field is alpha-level and is only honored by servers that enable the NonPreemptingPriority feature.
+  // +optional
+  optional string preemptionPolicy = 5;
 }
 
 // PriorityClassList is a collection of priority classes.