kubeadm/join: expose the KubeConfigPath() method to joinData

[neolit123]

What this PR does / why we need it:

This fixes the following error:
"error execution phase control-plane-join/etcd:
control-plane-join phase invoked with an invalid data struct"

The problem here is that joinData cannot be type-asserted
to the interface type under controlplanejoin.go (controlPlaneJoinData)
because joinData lacks KubeConfigPath.

Given we use KubeConfigPath in more than one place for join
it makes sense to define the method and make it return:
kubeadmconstants.GetAdminKubeConfigPath()

Which issue(s) this PR fixes:

NONE

Special notes for your reviewer:
https://k8s-testgrid.appspot.com/sig-cluster-lifecycle-all#kubeadm-kind-master

Does this PR introduce a user-facing change?:

NONE

/kind bug
/priority critical-urgent
cc @fabriziopandini @RA489
cc @kubernetes/sig-cluster-lifecycle-pr-reviews

[BenTheElder]

/lgtm
thank you, one minor typo in a comment

[ereslibre]

This removal was fine, the problem is that the interface in controlplanejoin.go was not adapted, nor the code there after removing this unneeded method in join.go, so:

kubernetes/cmd/kubeadm/app/cmd/phases/join/controlplanejoin.go

Line 46 in ad403f8

KubeConfigPath() string

Removing KubeConfigPath function from the interface in the controlPlaneJoinData will allow the cast to happen, with the removal of KubeConfigPath on join.go as well (basically reverting this patch).

Then, all references on this phase need adapting and calling directly to kubeadmconstants.GetAdminKubeConfigPath() instead:

kubernetes/cmd/kubeadm/app/cmd/phases/join/controlplanejoin.go

Line 120 in ad403f8

kubeConfigFile := data.KubeConfigPath()

kubernetes/cmd/kubeadm/app/cmd/phases/join/controlplanejoin.go

Line 162 in ad403f8

kubeConfigFile := data.KubeConfigPath()

kubernetes/cmd/kubeadm/app/cmd/phases/join/controlplanejoin.go

Line 190 in ad403f8

kubeConfigFile := data.KubeConfigPath()

The problem was that KubeConfigPath() was removed from join.go but not adapted in controlplanejoin.go afterwards, so the cast fails because joinData does not implement the required KubeConfigPath function in the controlPlaneJoinData interface: all of them should be removed and use kubeadmconstants.GetAdminKubeConfigPath() instead.

cc/ @neolit123 @fabriziopandini @rosti @RA489

[neolit123]

/retest

the cast fails because joinData does not implement the required KubeConfigPath function in the controlPlaneJoinData interface: all of them should be removed and use kubeadmconstants.GetAdminKubeConfigPath() instead.

@ereslibre given the kubeconfig is used in more than one place in join.go and controlplanejoin.go i think it's fine to have the public joinData.KubeConfigPath() helper even if it only returns kubeadmconstants.GetAdminKubeConfigPath()

[fabriziopandini]

@neolit123 thanks for the quick investigation on this problem
Eventually we will reconsider this in the audit of join phases
/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabriziopandini, neolit123

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