rbd: skip the copyup when an entire object writing
rbd: skip the copyup when an entire object writing

It need to copyup the parent's content when layered writing,
but an entire object write would overwrite it, so skip it.

Signed-off-by: Guangliang Zhao <a640ecc6a565666c11fd65fb44c17459dc60b214@gmail.com>
Reviewed-by: Josh Durgin <51652c783f70f5b272ebd02f1fd20d3af7a2449f@inktank.com>
Reviewed-by: Alex Elder <f429030cf5c0faf36fac3d102073b6e63a647baa@linaro.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs