Add workers to buildkite

.buildkite/pipeline.yml

@@ -44,6 +44,31 @@ steps:
       - docker#v3.0.1:
           image: "python:3.6"
 
+  - label: "SyTest - :python: 2.7 / :postgres: 9.6 / Workers"
+    agents:
+      queue: "medium"
+    env:
+      POSTGRES: "1"
+      WORKERS: "1"
+    command:
+      - "bash .buildkite/merge_base_branch.sh"
+      - "bash /synapse_sytest.sh"
+    plugins:
+      - docker#v3.0.1:
+          image: "matrixdotorg/sytest-synapse:dinsic-test"
+          propagate-environment: true
+          always-pull: true
+          workdir: "/src"
+          entrypoint: "/bin/sh"
+          init: false
+          shell: ["-x", "-c"]
+          mount-buildkite-agent: false
+          volumes: ["./logs:/logs"]
+      - artifacts#v1.2.0:
+          upload: [ "logs/**/*.log", "logs/**/*.log.*", "logs/results.tap" ]
+      - matrix-org/annotate:
+          path: "logs/annotate.md"
+          style: "error"
 
   - label: "SyTest - :python: 2.7 / :postgres: 9.6 / Monolith"
     agents: