Remove 'desc' from docker creation attribute

"Docker run" API do not support adding description for
a container, so we can remove 'desc' from docker creation
attribute.

Change-Id: Ic2c0c0c17bb5e25ab727a3e6469ebee802c1683f

magnumclient/tests/v1/test_shell.py

@@ -22,7 +22,7 @@ from magnumclient.v1 import shell
 
 container_fixture = {
     "name": "container",
-    "desc": "container description."
+    "image_id": "image_id"
 }