monitor: Switch from timer_new() to timer_new_ns()

We don't actually care for the scale, so we can just as well use the
simpler interface.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1444921716-9511-4-git-send-email-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>