* 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
* mw/kubernetes: move fallthrough tests out
Remove the testcase duplication and put fallthrough tests in separate
file.
Also make some names shorter and more descriptive.
* fix test build
* fix corefile