Fix error on exiting

[huiwq1990]

What this PR does / why we need it:

When use kubefedctl join cluster setting error-on-existing=false and secret-name have specify value, it will case secret exist error. Join command demo:

kubefedctl join newdev --cluster-context newdev --host-cluster-context minikube --kubefed-namespace tpaas-federation --secret-name=minikube-newdev --error-on-existing=false -v 2

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

[huiwq1990]

/assign @jimmidyson

[makkes]

I don't fully agree with the changes proposed herein as I believe the semantics and the implementation should be simpler:

• If --error-on-existing is set to true and the secret exists, return an error.
• If --error-on-existing is set to false and the secret exists, just update it.

My main concern is around the update logic that you're introducing here which in my opinion makes the interface more complicated for users to reason about (adding annotations) and error-prone, basically something that might not work as expected.

So in my humble opinion just updating the secret in any case if error-on-existing is set to false is just simpler and less error-prone.

[huiwq1990]

@makkes if we don't auto trigger clustercontroller reconcile, the joinedcluster will use old token until it restart or somethingelse trigger reconcile, it will confuse user find real reason if the token not work .

[fejta-bot]

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[hectorj2f]

/remove-lifecycle stale

[makkes]

maybe @hectorj2f or @jimmidyson might want to chime in here as well.

[makkes]

/lgtm

[hectorj2f]

/lgtm

[hectorj2f]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hectorj2f, huiwq1990, makkes

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