dump: Turn some functions to void to make code cleaner

Functions shouldn't return an error code and an Error object at the same time.
Turn all these functions that returning Error object to void.
We also judge if a function success or fail by reference to the local_err.

Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>