[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/apimachinery/pkg/apis/meta/v1/conversion.go b/vendor/k8s.io/apimachinery/pkg/apis/meta/v1/conversion.go
index 5c36f82..d07069e 100644
--- a/vendor/k8s.io/apimachinery/pkg/apis/meta/v1/conversion.go
+++ b/vendor/k8s.io/apimachinery/pkg/apis/meta/v1/conversion.go
@@ -77,6 +77,8 @@
 		Convert_Slice_string_To_Slice_int32,
 
 		Convert_Slice_string_To_v1_DeletionPropagation,
+
+		Convert_Slice_string_To_v1_IncludeObjectPolicy,
 	)
 }
 
@@ -317,3 +319,11 @@
 	}
 	return nil
 }
+
+// Convert_Slice_string_To_v1_IncludeObjectPolicy allows converting a URL query parameter value
+func Convert_Slice_string_To_v1_IncludeObjectPolicy(input *[]string, out *IncludeObjectPolicy, s conversion.Scope) error {
+	if len(*input) > 0 {
+		*out = IncludeObjectPolicy((*input)[0])
+	}
+	return nil
+}