[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/client-go/tools/auth/OWNERS b/vendor/k8s.io/client-go/tools/auth/OWNERS
index c607d2a..3e05d30 100644
--- a/vendor/k8s.io/client-go/tools/auth/OWNERS
+++ b/vendor/k8s.io/client-go/tools/auth/OWNERS
@@ -1,3 +1,5 @@
+# See the OWNERS docs at https://go.k8s.io/owners
+
 approvers:
 - sig-auth-authenticators-approvers
 reviewers:
diff --git a/vendor/k8s.io/client-go/tools/auth/clientauth.go b/vendor/k8s.io/client-go/tools/auth/clientauth.go
index 20339ab..c341726 100644
--- a/vendor/k8s.io/client-go/tools/auth/clientauth.go
+++ b/vendor/k8s.io/client-go/tools/auth/clientauth.go
@@ -105,7 +105,7 @@
 // The fields of client.Config with a corresponding field in the Info are set
 // with the value from the Info.
 func (info Info) MergeWithConfig(c restclient.Config) (restclient.Config, error) {
-	var config restclient.Config = c
+	var config = c
 	config.Username = info.User
 	config.Password = info.Password
 	config.CAFile = info.CAFile
@@ -118,6 +118,7 @@
 	return config, nil
 }
 
+// Complete returns true if the Kubernetes API authorization info is complete.
 func (info Info) Complete() bool {
 	return len(info.User) > 0 ||
 		len(info.CertFile) > 0 ||