core: update sound device on next run VM snapshot

* Added an 'EditableDeviceOnVmStatusField' annotation for
  'soundDeviceEnabled' (in VmManagementParametersBase).
* Consequently, removed canDo validation in UpdateVmCommand.

Change-Id: Icb794bcb6a054bbb0424c35f024c4a1a85ea5069
Bug-Url: https://bugzilla.redhat.com/1035289
Signed-off-by: Daniel Erez <derez@redhat.com>