Add Makefile for running tests in Docker

It assumes you've got Docker running on /var/run/docker.sock, but
that should be the case on both Linux and in Boot2Docker.
Signed-off-by: Ben Firshman <ben@firshman.co.uk>

Makefile

+.PHONY: all build test integration-test unit-test
+
+all: test
+
+build:
+	docker build -t docker-py .
+
+test: unit-test integration-test
+
+unit-test: build
+	docker run docker-py python tests/test.py
+
+integration-test: build
+	docker run -v /var/run/docker.sock:/var/run/docker.sock docker-py python tests/integration_test.py
+