Remove generate tests and use static test yaml. (#515)

* Remove generate tests and use static test yaml.

Since there aren't any more variables in the test yaml, replace
the shell script with a static YAML.

* Print python version

* Remove generate test step

tests/docker-test.yaml

@@ -0,0 +1,10 @@
+version: '2'
+
+services:
+  mailman-core:
+    image: maxking/mailman-core:rolling
+
+  mailman-web:
+    image: maxking/mailman-web:rolling
+    environment:
+    - SECRET_KEY=abcdefghijklmnopqrstuv