* Rename middleware to plugin
first pass; mostly used 'sed', few spots where I manually changed
text.
This still builds a coredns binary.
* fmt error
* Rename AddMiddleware to AddPlugin
* Readd AddMiddleware to remain backwards compat
* Remove debug from interface and methods
* remove debug queries from etcd
* remove debug queries from k8s - they were not used
* And remove from mw/proxy-google as well
* Remove debug query test
* middleware/proxy: absorb httpproxy
Move the httproxy into proxy. This adds and Exchanger interface which
is used to exchange the messages with the upstream.
The https_google upstream will re-resolve itself and update the upstream
hosts used every 300s.
* Remove and add TODO
