test/util: Add mini DNS server for testing purposes

This is a mini-DNS server for testing purposes.

This can be used to set up hermetic tests in containers, and work around
glibc's limitation of being unable to create per-process host aliases.

test/util/lib.sh

@@ -107,6 +107,10 @@ function conngen() {
 	go run ${UTILDIR}/conngen.go "$@"
 }
 
+function minidns() {
+	go run ${UTILDIR}/minidns.go "$@"
+}
+
 function success() {
 	echo success
 }