correctly implement volumes_from property

The Docker plugin incorrectly implements the 'volumes_from' option:

- The property is marked as a string when it should be a list, and
- The property needs to be passed to start_container rather than
  create_container.

Change-Id: I617a4d29a9edbb45d80c7b8abb8f87eeaf795a8b
closes-bug: #1364041
closes-bug: #1364039
Merge "correctly implement volumes_from property"