Remove references to kubeadm specific locations for kubeconfig.

[davidewatson]

Also pass --requestheader-client-ca-file to fix https://goo.gl/qZqmMb

What this PR does / why we need it:
The current apiserver manifest used by the shared deployer code makes assumptions which are not true for non-kubeadm created clusters. This causes problems when clusterctl and minikube are not used together unless the bootstrapping cluster was also created with kubeadm.

It may not be necessary to fix this given #409

This PR is mainly for documentation purposes for now.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[davidewatson]

/hold

[roberthbailey]

@davidewatson - is this obsoleted by #494?

[davidewatson]

It has been. Thanks for reminding me!

/close

[k8s-ci-robot]

@davidewatson: Closing this PR.

In response to this:

It has been. Thanks for reminding me!

/close

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