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/examples/eg_attach.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env python3
-"""Example: Run Alpine container and attach."""
+"""Example: Run top on Alpine container."""
 
 import podman
 
@@ -8,10 +8,11 @@ print('{}\n'.format(__doc__))
 with podman.Client() as client:
     id = client.images.pull('alpine:latest')
     img = client.images.get(id)
-    cntr = img.create()
-    cntr.start()
+    cntr = img.create(detach=True, tty=True, command=['/usr/bin/top'])
+    cntr.attach(eot=4)
 
     try:
-        cntr.attach()
-    except BrokenPipeError:
-        print('Container disconnected.')
+        cntr.start()
+        print()
+    except (BrokenPipeError, KeyboardInterrupt):
+        print('\nContainer disconnected.')