Shuffle some deck-chairs

* Move everything under .buildkite/
* Make ruby version selectable

Author: matthewd

.buildkite/Dockerfile

@@ -0,0 +1,18 @@
+ARG RUBY_IMAGE
+FROM ${RUBY_IMAGE:-ruby:latest}
+
+RUN which git >/dev/null || ( \
+  apt-get update && \
+  DEBIAN_FRONTEND=noninteractive apt-get install --no-install-recommends -y \
+    git \
+  )
+
+ENV JRUBY_OPTS="--dev -J-Xmx400M"
+
+RUN mkdir /app
+WORKDIR /app
+
+ADD Gemfile Gemfile.lock /app/
+RUN bundle install -j 8
+
+ADD . /app

.buildkite/docker-compose.yml

@@ -0,0 +1,11 @@
+version: "3.6"
+
+services:
+  app:
+    build:
+      context: ../
+      dockerfile: .buildkite/Dockerfile
+      args:
+        - RUBY_IMAGE
+    environment:
+      - CI

.buildkite/pipeline.yml

@@ -1,6 +1,14 @@
-steps:
-  - name: ":rspec:"
-    command: "rspec --color specs"
+_templates:
+  - &base
     plugins:
       docker-compose#v2.6.0:
         run: app
+        config: .buildkite/docker-compose.yml
+    timeout_in_minutes: 10
+
+steps:
+  - <<: *base
+    name: ":rspec:"
+    command: "rspec --color specs"
+    env:
+      RUBY_IMAGE: "ruby:2.5"