Automatic merge from submit-queue (batch tested with PRs 60148, 60022, 59125, 60068, 60154). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Refactor kubeadm join command generation

**What this PR does / why we need it**:
Creation of the `kubeadm join` command is implemented in three different points of kubeadm:
- `kubeadm init`
- `kubeadm token create`
- `kubeadm phase bootstrap-token create`

This PR refactor above points in order to share a common function for creating the `kubeadm join` command.

**Which issue(s) this PR fixes**:
Fixes [#567](https://github.com/kubernetes/kubeadm/issues/567)

**Special notes for your reviewer**:
While implementing the PR, I changed the order of parameters in `kubeadm join` from:

```
  kubeadm join --token 8df4zm.5jyv2nrxb18y84jq 172.31.0.101:6443 --discovery-token-ca-cert-hash sha256:b62e1f70c1c6afebe36bc971b15b90f7e453f1c0fe2ddc4d92e07512f1143194
```

to

```
  kubeadm join 172.31.0.101:6443 --token 8df4zm.5jyv2nrxb18y84jq --discovery-token-ca-cert-hash sha256:b62e1f70c1c6afebe36bc971b15b90f7e453f1c0fe2ddc4d92e07512f1143194
```

**Release note**:
```release-note
NONE
```