Switch to Buildkite beta agent

Fixes operable/cog#1280

Author: christophermaier

.buildkite/pipeline.yml

@@ -1,9 +1,9 @@
-env:
-  BUILDKITE_DOCKER: true
-  BUILDKITE_DOCKER_FILE: Dockerfile.ci
-
 steps:
-  - command: make test
-    label: ":go: Unit Tests"
+  - label: ":go: Unit Tests"
+    command: make test
+    plugins:
+      docker-compose:
+        run: test
+        config: docker-compose.ci.yml
     agents:
-      - docker=1.12.1
+      queue: beta

docker-compose.ci.yml

@@ -0,0 +1,6 @@
+version: '2'
+services:
+  test:
+    build:
+      context: .
+      dockerfile: Dockerfile.ci