restapi: Control\view Soundcard property

* Added 'soundcard_enabled' property to REST VM/template/vmpool resource
  (accessible via 'All-Content' header)
* Added support for property in:
  VM/Template/Instance - Add / Update
  Pool - Add
* Updated rsdl
* Updated tests

Change-Id: I598cf89b6a5fd4755958cf7b597484c225166460
Bug-Url: https://bugzilla.redhat.com/1021186
Signed-off-by: Eldan Shachar <eshachar@redhat.com>