Send 400 error if device specification contains unexpected attributes

Bug #1171926

This patch simply enhances the validator for the 'devices' attribute
by verifying each element in the device list does not contain
unexpected attributes.

Change-Id: Id3fd182a7f711b482ad371752983264ad73b100f
Imported Translations from Transifex

Change-Id: Ica3123c46290d48cc344e0f99a71be7307aed8e5
Merge "Send 400 error if device specification contains unexpected attributes"