mw/file: add include test (#960)
mw/file: add include test (#960)

$INCLUDE was fixed in miekg/dns, create tests in CoreDNS so that we know
we have the latest version.

Fixes #880
jremond/coredns,ii/coredns,coredns/coredns,jremond/coredns,chrisohaver/coredns,ii/coredns,miekg/coredns,miekg/coredns,yongtang/coredns,johnbelamaric/coredns,johnbelamaric/coredns