Make script/test use Docker

Really easy to run entire test suite with Docker now. Also switch
Wercker to use the same script.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>

wercker.yml

@@ -4,12 +4,6 @@ build:
     - script:
         name: validate DCO
         code: script/validate-dco
-    - script:
-        name: build
-        code: docker build -t fig .
-    - script:
-        name: flake8
-        code: docker run -v /var/run/docker.sock:/var/run/docker.sock fig flake8 fig
     - script:
         name: run tests
-        code: docker run -v /var/run/docker.sock:/var/run/docker.sock fig nosetests
+        code: script/test