Add py27-old test case to buildkite

.buildkite/pipeline.yml

@@ -90,6 +90,17 @@ steps:
           image: "python:3.7"
           propagate-environment: true
 
+  - command:
+      - "python -m pip install tox"
+      - "tox -e py27-old,codecov"
+    label: ":python: 2.7 / SQLite / Old Deps"
+    env:
+      TRIAL_FLAGS: "-j 2"
+    plugins:
+      - docker#v3.0.1:
+          image: "python:2.7"
+          propagate-environment: true
+
   - label: ":python: 2.7 / :postgres: 9.4"
     env:
       TRIAL_FLAGS: "-j 4"