actual error will be present in the stdErr not the error
when we try to add a task to flatten the rbd image. This
commits corrects the error checking when the image does
not have a parent.
Signed-off-by: Madhu Rajanna <madhupr007@gmail.com>
(cherry picked from commit 05b8433b89c3583b6c921bd831af19c6de68ec88)