Defining test sandbox in compose file allows testing against multi node swarm setup (#591)

* Defining test sandbox in compose file allows swapping with multi node swarm setup

* Test cases can request a multi node swarm cluster

* Docker healthchecks can be used for awaiting ready state

* Compose profiles can be used

test/docker-compose.yml

@@ -0,0 +1,27 @@
+services:
+  manager: &node
+    privileged: true
+    image: offen/docker-volume-backup:test-sandbox
+    healthcheck:
+      test: ["CMD", "docker", "info"]
+      interval: 1s
+      timeout: 5s
+      retries: 50
+    volumes:
+      - $SOURCE:/code
+      - $TARBALL:/cache/image.tar.gz
+      - docker_volume_backup_test_sandbox_image:/var/lib/docker/image
+      - docker_volume_backup_test_sandbox_overlay2:/var/lib/docker/overlay2
+
+  worker1:
+    <<: *node
+    profiles:
+      - multinode
+  worker2:
+    <<: *node
+    profiles:
+      - multinode
+
+volumes:
+  docker_volume_backup_test_sandbox_image:
+  docker_volume_backup_test_sandbox_overlay2: