Fix pip install in unit test container

The SWIG_FEATURES environment variable is to get pip install working with M2Crypto==0.22.3. It works without SWIG_FEATURES if we update to M2Crypto >= 0.23.0.

Also did some organization, add README.

tools/docker-compose/unit-tests/docker-compose.yml

@@ -0,0 +1,13 @@
+---
+version: '2'
+services:
+  unit-tests:
+    build:
+      context: ../../../
+      dockerfile: tools/docker-compose/unit-tests/Dockerfile
+    environment:
+      SWIG_FEATURES: "-cpperraswarn -includeall -I/usr/include/openssl"
+    command: ["make requirements_test test"]
+
+    volumes:
+      - ../../../:/ansible-tower