k8s: Validate API server excluded admission plugins

k8s: Validate API server excluded admission plugins

This patch verifies if CIS Kubernetes Benchmark v1.3.0 section
regarding master node configuration is satisfied (1.1.10).

However, CIS Kubernetes Benchmark v1.3.0 mismatches official
documentation: Kubernetes 1.10+ already provides safe defaults from
security standpoint [1] (ONAP Casablanca uses 1.11).

Deprecated admission control plugin flag has also been validated since
it was still available in Kubernetes provided by Rancher [2].

[1] https://kubernetes.io/docs/reference/access-authn-authz/admission-controllers/#is-there-a-recommended-set-of-admission-controllers-to-use
[2] https://github.com/rancher/rancher/issues/15064

Issue-ID: SECCOM-235
Change-Id: I0e8fe9f885861f155cb8265df085fa93dbdff6d2
Signed-off-by: Pawel Wieczorek <p.wieczorek2@samsung.com>