docs: update manpage for stderr->log rename
With commit ed7f5f1d8db06fc31352a5ef4f54985e630c575a the name of
this backend changed from “stderr” to “log”.
Signed-off-by: Philipp Gesang <philipp.gesang@intra2net.com>
Message-id: 20170202114101.2655-1-philipp.gesang@intra2net.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
authored by