[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/klog/SECURITY_CONTACTS b/vendor/k8s.io/klog/SECURITY_CONTACTS
index 520ddb5..6128a58 100644
--- a/vendor/k8s.io/klog/SECURITY_CONTACTS
+++ b/vendor/k8s.io/klog/SECURITY_CONTACTS
@@ -1,10 +1,10 @@
 # Defined below are the security contacts for this repo.
 #
-# They are the contact point for the Product Security Team to reach out
+# They are the contact point for the Product Security Committee to reach out
 # to for triaging and handling of incoming issues.
 #
 # The below names agree to abide by the
-# [Embargo Policy](https://github.com/kubernetes/sig-release/blob/master/security-release-process-documentation/security-release-process.md#embargo-policy)
+# [Embargo Policy](https://git.k8s.io/security/private-distributors-list.md#embargo-policy)
 # and will be removed and replaced if they violate that agreement.
 #
 # DO NOT REPORT SECURITY VULNERABILITIES DIRECTLY TO THESE NAMES, FOLLOW THE