Fix Horizon crash when parsing volume list

If using Nova or Cinder CLI to create a new volume
(without name) that can be used to boot a new VM,
then Horizon will be crashed when the volume list
is retrieved by clicking the tab "Volumes" on
Horizon dashboard.

Change-Id: I9850dca2f6f5ab8eebab035f9e7cf19d7262f7d2
Closes-Bug: #1389108
Merge "Fix Horizon crash when parsing volume list"