qemu-io: Use error_[gs]et_progname()

qemu-io reimplements itself what
error_get_progname()/error_set_progname() already does.
This commit switches it to use this API from qemu-error.h

Signed-off-by: Christophe Fergeau <cfergeau@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20190131164614.19209-2-cfergeau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>