Add docker-check-updates to check for updates in Docker images

docker-check-updates

@@ -0,0 +1,21 @@
+#!/usr/bin/python
+"""Check Docker images for security/distro updates. Assumes DNF."""
+
+from __future__ import division, print_function
+from docker import Client
+import subprocess
+
+c = Client(base_url='unix://var/run/docker.sock')
+for container in c.containers():
+  name = container['Names'][0]
+  id_ = container['Id']
+  image_id = c.inspect_container(id_)['Image']
+
+  print('Container: {}'.format(name))
+  print('Image: {} '.format(image_id))
+
+  # Not using the API here for simplicity (for now)
+  subprocess.call(['docker', 'run', '-t', '--rm',
+                   image_id,
+                   '/bin/bash', '-c',
+                   'dnf -q check-update; if [ $? == 100 ]; then echo "Updates available"; fi'])