Automatic merge from submit-queue
Add node-name flag to `join` phase
**What this PR does / why we need it**: Allow to specify a node-name instead of relaying in `os.Hostname()`
This is useful where kubelet use the name given by the cloud-provider to
register the node.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: partially fixeskubernetes/kubeadm#64
**Special notes for your reviewer**:
**Release note**:
```release-note
Added new flag to `kubeadm join`: --node-name, that lets you specify the name of the Node object that's gonna be created
```
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