Due to a change in Go 1.10.3[1], which k8s v1.11.1 is based on, now
magnum is failing to create a working k8s cluster with version 1.11.1.
This patch is changing removing the extention usage for server auth
for ca cert and using simple public/private keys for k8s service account
keys.
[1] https://go.googlesource.com/go/+/09fa131c99da0ef9f78c9f4f6cd955237ccc01cd
Task: 23210
Story: 2003103
Change-Id: Ieba8f55d55db2afda6888d4bc6c2caa87370d13d