mr_create: fix output messages
mr_create: fix output messages

`errors.Wrapf()` was being used within `log.Fatal()` calls, but it's not the
correct way of doing it. The first adds a message to the error and return
_another_ error if something goes wrong, but if the messages is added
correctly, it returns <nil>. So, whenever this errors were printed, `<nil>`
was being prompted to the user.

Signed-off-by: Bruno Meneguele <82c7731bc2625bcbab88bc571aee6631ba3f66f3@redhat.com>

zaquestion/lab,zaquestion/lab