Add support for Windows worker nodes

[benmoss]

What this PR does / why we need it: This PR adds support for deploying Windows worker nodes.

• Adds property to flanneld to switch to hostgw networking, but still defaults to overlay to keep backwards compatibility.
• Adds windows versions of flanneld, cni-plugins, and kubernetes binaries. The start scripts are translated from the Linux versions.
• Because Windows has two base images (nanoserver and servercore), the nodes pull these images on start up. (So containers start quickly, even if they're scheduled to a brand new node.) This means that there is a hard coded value specific to a version of windows. Currently, that version is 1803.

How can this PR be verified? There is a PR to kubo-ci that adds a test that schedules a windows pod. With this PR and the one to kubo-deployment, the test passes.

Is there any change in kubo-deployment? Yes Is there any change in kubo-ci? Yes Does this affect upgrade, or is there any migration required? No, the only linux changes is a new spec option for flannel backend type, and the default maintains current behavior. Which issue(s) this PR fixes: Lack of windows support Release note:

Adds support for windows workers.

[cfdreddbot]

:white_check_mark: Hey benmoss! The commit authors and yourself have already signed the CLA.