Makefile: initial commit with 'docker-dns-test'

For etcd-io#8502.
First step to make DNS/SRV tests easier to run.

```
make docker-dns-test-build
make docker-dns-test
```

Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>

Makefile

@@ -0,0 +1,47 @@
+# gcloud docker -- login -u _json_key -p "$(cat /etc/gcp-key-etcd.json)" https://gcr.io
+
+.PHONY: build
+build:
+	GO_BUILD_FLAGS="-v" ./build
+	rm -rf ./gopath
+	./bin/etcd --version
+	ETCDCTL_API=3 ./bin/etcdctl version
+
+docker-test-build:
+	docker build --tag gcr.io/etcd-development/etcd-test:latest --file ./Dockerfile-test .
+
+docker-test-push:
+	gcloud docker -- push gcr.io/etcd-development/etcd-test:latest
+
+docker-test:
+	docker run \
+		--rm \
+		--volume=`pwd`:/go/src/github.com/coreos/etcd \
+		gcr.io/etcd-development/etcd-test:latest \
+		/bin/bash -c "RELEASE_TEST=y INTEGRATION=y PASSES='build unit release integration_e2e functional' ./test 2>&1 | tee docker-test.log"
+
+docker-dns-test-build:
+	docker build \
+		--tag gcr.io/etcd-development/etcd-dns-test:latest \
+		--file ./e2e/docker/Dockerfile \
+		./e2e/docker
+
+	# compile with debian base image
+	docker run \
+		--rm \
+		--volume=`pwd`/:/etcd \
+		gcr.io/etcd-development/etcd-dns-test:latest \
+		/bin/bash -c "pushd /etcd && GO_BUILD_FLAGS=-v ./build && popd && /etcd/bin/etcd --version"
+
+docker-dns-test-push:
+	gcloud docker -- push gcr.io/etcd-development/etcd-dns-test:latest
+
+docker-dns-test:
+	docker run \
+		--rm \
+		--tty \
+		--dns 127.0.0.1 \
+		--volume=`pwd`/bin:/etcd \
+		--volume=`pwd`/integration/fixtures:/certs \
+		gcr.io/etcd-development/etcd-dns-test:latest \
+		/bin/bash -c "pushd /etcd && /run.sh && rm -rf infra*.etcd && popd"

e2e/docker/Dockerfile

@@ -1,12 +1,18 @@
 FROM golang:1.9-stretch
 LABEL Description="Image for etcd DNS testing"
-RUN apt update -y
-RUN go get github.com/mattn/goreman
-RUN apt install -y bind9
+
+RUN apt update -y \
+  && apt install -y \
+  bind9 \
+  dnsutils
+
 RUN mkdir /var/bind
 RUN chown bind /var/bind
 ADD Procfile.tls /Procfile.tls
 ADD run.sh /run.sh
+
 ADD named.conf etcd.zone rdns.zone /etc/bind/
 ADD resolv.conf /etc/resolv.conf
-CMD ["/run.sh"]
+
+RUN go get github.com/mattn/goreman
+CMD ["/run.sh"]