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 fixes kubernetes/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
```