Updated Makefile to help with release testing

Makefile

-.PHONY: all build test integration-test unit-test
+.PHONY: all build test integration-test unit-test build-py3 unit-test-py3 integration-test-py3
 
 HOST_TMPDIR=test -n "$(TMPDIR)" && echo $(TMPDIR) || echo /tmp
 
@@ -7,10 +7,19 @@ all: test
 build:
 	docker build -t docker-py .
 
-test: unit-test integration-test
+build-py3:
+	docker build -t docker-py3 -f Dockerfile-py3 .
+
+test: unit-test integration-test unit-test-py3 integration-test-py3
 
 unit-test: build
 	docker run docker-py python tests/test.py
 
+unit-test-py3: build-py3
+	docker run docker-py3 python tests/test.py
+
 integration-test: build
 	docker run -e NOT_ON_HOST=true -v `$(HOST_TMPDIR)`:/tmp -v /var/run/docker.sock:/var/run/docker.sock docker-py python tests/integration_test.py
+
+integration-test-py3: build-py3
+	docker run -e NOT_ON_HOST=true -v `$(HOST_TMPDIR)`:/tmp -v /var/run/docker.sock:/var/run/docker.sock docker-py3 python tests/integration_test.py