Add migration warning and option to migrate to labels.

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

tests/integration/migration_test.py

@@ -0,0 +1,23 @@
+import mock
+
+from compose import service, migration
+from compose.project import Project
+from .testcases import DockerClientTestCase
+
+
+class ProjectTest(DockerClientTestCase):
+
+    def test_migration_to_labels(self):
+        web = self.create_service('web')
+        db = self.create_service('db')
+        project = Project('composetest', [web, db], self.client)
+
+        self.client.create_container(name='composetest_web_1', **web.options)
+        self.client.create_container(name='composetest_db_1', **db.options)
+
+        with mock.patch.object(service, 'log', autospec=True) as mock_log:
+            self.assertEqual(project.containers(stopped=True), [])
+            self.assertEqual(mock_log.warn.call_count, 2)
+
+        migration.migrate_project_to_labels(project)
+        self.assertEqual(len(project.containers(stopped=True)), 2)

tests/unit/container_test.py

@@ -28,7 +28,7 @@ class ContainerTest(unittest.TestCase):
                 "Labels": {
                     "com.docker.compose.project": "composetest",
                     "com.docker.compose.service": "web",
-                    "com.docker.compose.container_number": 7,
+                    "com.docker.compose.container-number": 7,
                 },
             }
         }