Use fabric API to execute subtasks in docker.clean

docker.py

 from __future__ import unicode_literals
 
-from fabric.api import task, roles, env, local, run, lcd
+from fabric.api import task, roles, env, local, run, lcd, execute
 from fabric.colors import red, green
 from fabric.contrib.console import confirm
 
@@ -231,9 +231,9 @@ def clean():
             red('This will stop, remove container and delete docker image ' +
                 'related to this project. Do you want to continue?'),
             default=False)):
-        container_stop()
-        container_remove()
-        image_remove()
+        execute(container_stop)
+        execute(container_remove)
+        execute(image_remove)
 
 
 @task