Refactor: libcib: Clean up update_cib_object() and add_cib_object()

update_cib_object has only two callers: itself and add_cib_object().
add_cib_object() does all the top-level validation, including making
sure an object with the same name (and ID if given) doesn't already
exist.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>