Add docker-compose to requirements

Use requirements ranges to avoid having to update the requirements file too frequently. Also adds a Make target for installing requirements.

Makefile

@@ -17,3 +17,6 @@ devstack.start:     ## Start all services
 
 devstack.stop:      ## Stop all services
 	docker-compose stop
+
+requirements:       ## Install requirements
+	pip install -r requirements.txt

requirements.txt

-PyYAML==3.12
+docker-compose>=1.9.0,<2.0.0
+PyYAML>=3.12,<4.0