Docs munge infrastructure

First version of Introspection and Debugging section of User Guide.

Automatically open a firewall when creating a GCE load balancer.

add user guide docs for kubectl exec, proxy, and port-forward

V0.21.2 merge to master

Run all munges on all docs

LimitRange example improvements, detailed README

Fix kubelet.md with --max-pods

add spec.host as a synonym for spec.nodeName in v1

(cherry picked from commit 63c73a58)

Rather than terminating, Collect the errors and print them per-file-per-munge.

This reverts commit baf92e62.

Fix gofmt from #11084

Change the generated release template to docs/README.md

Robustly cleanup MIG template on GCE teardown

Change kubelet flag --max-pods default value to 40 to match v1.0 roadmap

Automated cherry pick of #11084

update kubectl output in examples

Add GKE coverage for e2e tests that support both GCE and GKE

Rather than terminating, Collect the errors and print them per-file-per-munge.

Allow upgrade target version to be specified

Add user guide for connecting applications

First draft of deployment-oriented sections of the user guide.