add roles to narwal[5-7] and fill known_hosts file
    
    narwal5 will become the "static master" (doing git pull and keeping all
    narwals up to date), and also is one of the static.o.o webservers.
    
    narwal6 and narwal7 will "only" be webservers.
    
    Also add the SSH host pubkeys to known_hosts of static_master.