core: remove unnecessary allocation of Guid

Remove unnecessary allocation and cloning of Guid
when assigning id values to objects.
Removed cloning in 2 places, in third place its usage
was in unused method, so removed the method.

Change-Id: I857b4fe7ad1f1dcff486e489e262441823a6cb3e
Signed-off-by: Alissa Bonas <abonas@redhat.com>