Refactor attach()/start() after podman changes

* Update examples
* Update/Clean up unittests
* Add Mixins for container attach()/start()

Signed-off-by: Jhon Honce <jhonce@redhat.com>

Closes: #1080
Approved by: baude

contrib/python/test/test_images.py

@@ -62,6 +62,7 @@ class TestImages(PodmanTestCase):
         actual = self.alpine_image.container()
         self.assertIsNotNone(actual)
         self.assertEqual(actual.status, 'configured')
+
         ctnr = actual.start()
         self.assertIn(ctnr.status, ['running', 'exited'])