Fixed drag and drop of unplaced units.
Merge branch 'fix-drop-unit' into fix-drop-unit-landing
Merge pull request #351 from huwshimi/fix-drop-unit-landing

Drag and drop of unplaced units was broken. This fixes it.

Bug: https://bugs.launchpad.net/juju-gui/+bug/1323199

QA:

drag a service to the canvas
open the machine view
drag the unplaced unit to 'create a machine'
open the javascript console and check there are no errors.
click deploy and confirm The unit should be on a new machine. Adding more units and dropping them on existing containers should work as well.