Automatic merge from submit-queue (batch tested with PRs 49017, 45440, 48384, 45894, 48808)

kubeadm: Make kube-proxy tolerate the uninitialized cloud taint

**What this PR does / why we need it**:

This is needed in order to start the cloud-controller-manager successfully. The cloud controller manager should run as a DaemonSet with a nodeSelector for master nodes. The cloud controller manager should run on the hostNetwork to avoid the bootstrap problem when there is no CNI network yet. But the cloud controller manager needs to know how to address the master. It does this by talking to the kubernetes service (e.g. 10.96.0.1). That iptables rule must exist at the time, which now isn't the case when kube-proxy isn't running. kube-proxy isn't running due to that the kubelet is tainted with the external cloud taint.

This PR makes kube-proxy tolerate the cloud taint, so that the cloud controller manager can run easily on kubeadm clusters.

This was found by @prydie, thanks! 

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #

**Special notes for your reviewer**:

This should probably be a cherrypick candidate so folks can use kubeadm to easily create external cloud clusters. The change is small and isolated.

cc @wojtek-t 

**Release note**:

```release-note
kubeadm: Make kube-proxy tolerate the external cloud provider taint so that an external cloud provider can be easily used on top of kubeadm
```
cc @kubernetes/sig-cluster-lifecycle-pr-reviews @wlan0 @thockin