fix kubeadm init output

[fabriziopandini]

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PR fixes a duplicated message in the kubeadm init output (You can now join any number of machines by running the following on each node as root repeated twice) and wrong indentation.

Additionally, now the join control-plane message is printed only when the preconditions for joining a control plane are satisfied:

kubeadm init output for cluster WITHOUT controlPlaneEndpoint --> join control-plane conditions not satisfied:

....
Then you can join any number of worker nodes by running the following on each as root:

kubeadm join 172.17.0.2:6443 --token abcdef.0123456789abcdef \
    --discovery-token-ca-cert-hash sha256:4d170b1dfb24229319e0439a052b3cb56d02b152fc5903a4e4753e4fa76f8aca

kubeadm init output for cluster WITH controlPlaneEndpoint, but created WITHOUT --upload-certs

....
You can now join any number of control-plane node by copying certificate authorities
and service account keys on each node and then running the following as root:

  kubeadm join 172.17.0.2:6443 --token abcdef.0123456789abcdef \
    --discovery-token-ca-cert-hash sha256:c2b92b4d0864ed76706f51962ab709f404d58874f8a5b7e7e8aa88fcfe8fc518 \
    --experimental-control-plane

Then you can join any number of worker nodes by running the following on each as root:

kubeadm join 172.17.0.2:6443 --token abcdef.0123456789abcdef \
    --discovery-token-ca-cert-hash sha256:c2b92b4d0864ed76706f51962ab709f404d58874f8a5b7e7e8aa88fcfe8fc518

kubeadm init output for cluster WITH controlPlaneEndpoint and WITH --upload-certs

....
You can now join any number of the control-plane node running the following command on each as a root:

  kubeadm join 172.17.0.4:6443 --token abcdef.0123456789abcdef \
    --discovery-token-ca-cert-hash sha256:65034066a1b500506b6e673a70da433e171ebda9201f1f3e2767c68417bb44f6 \
    --experimental-control-plane --certificate-key 0123456789012345678901234567890123456789012345678901234567890123

Please note that the certificate-key gives access to cluster sensitive data, keep it secret!
As a safeguard, uploaded-certs will be deleted in two hours; If necessary, you can use
"kubeadm init phase upload-certs" to reload certs afterward.

Then you can join any number of worker nodes by running the following on each as root:

kubeadm join 172.17.0.4:6443 --token abcdef.0123456789abcdef \
    --discovery-token-ca-cert-hash sha256:65034066a1b500506b6e673a70da433e171ebda9201f1f3e2767c68417bb44f6

Does this PR introduce a user-facing change?:

kubeadm: the kubeadm init output now provides join control-plane example only when the preconditions for joining a control plane are satisfied

/sig cluster-lifecycle
/priority critical-urgent
/milestone v1.14
/assign @neolit123
/assign @timothysc
/cc @yagonobre

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabriziopandini

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[neolit123]

LGTM found two typo/nits.
thanks.

[fabriziopandini]

/test pull-kubernetes-kubemark-e2e-gce-big

[yagonobre]

Thanks @fabriziopandini

[xmudrii]

@fabriziopandini Hello! I'd like to remind that the Code Thaw is starting tomorrow, Tuesday PST EOD. Is it possible to get this PR reviewed and approved by then? Otherwise, the PR will have to compete with herd of other incoming PRs post-thaw.

[fabriziopandini]

@xmudrii thanks for the heads up. we are rallying to get this in before code thaw

@neolit123 @yagonobre, all the comment are addressed

[neolit123]

/lgtm

[neolit123]

/retest