Clear append admission plugins before inserting flags to kube-apiserver

[zetaab]

Currently when using appendAdmissionPlugins flag in kops configuration - it will also append that as flag to kube-apiserver. That will lead to result:

{"log":"error: unknown flag: --append-admission-plugins\n","stream":"stdout","time":"2019-06-24T10:21:40.176147035Z"}

(and kube-apiserver does not start)

cat /etc/kubernetes/manifests/kube-apiserver.manifest
...
  containers:
  - command:
    - /bin/sh
    - -c
    - mkfifo /tmp/pipe; (tee -a /var/log/kube-apiserver.log < /tmp/pipe & ) ; exec
      /usr/local/bin/kube-apiserver --allow-privileged=true --anonymous-auth=false
      --apiserver-count=3 --append-admission-plugins=PodSecurityPolicy

This PR will remove --append-admission-plugins flag if defined. This PR needs to be cherry-picked to release-1.14 and release-1.13

/kind bug

[robinpercy]

/test pull-kops-e2e-kubernetes-aws

[zetaab]

@robinpercy now the behaviour is what we need, and it works! It is not added to k8s apiserver manifest but the behaviour otherwise works as should.

[zetaab]

/test pull-kops-e2e-kubernetes-aws

[robinpercy]

@zetaab looks great. Have you been able to test to see why the e2e is failing?

[zetaab]

@robinpercy it is timing out, like many other PRs currently

@justinsb could we do something to this e2e aws test? It is really difficult to merge anything because its failing all the time

[zetaab]

/test pull-kops-e2e-kubernetes-aws

[zetaab]

/test pull-kops-e2e-kubernetes-aws

[robinpercy]

/test pull-kops-e2e-kubernetes-aws

[justinsb]

Thanks @zetaab

/approve
/lgtm

[zetaab]

@justinsb this needs to be backported to release-1.13 and release-1.14. Is there some easy way to do that or do I have to do PRs?

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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