Error helpfully on "letsencrypt --standalone"
Error helpfully on "letsencrypt --standalone"

 - Also refactor choose_configurator_plugins a bit

wteiken/letsencrypt,lmcro/letsencrypt,mitnk/letsencrypt,brentdax/letsencrypt,stweil/letsencrypt,TheBoegl/letsencrypt,brentdax/letsencrypt,jsha/letsencrypt,thanatos/lets-encrypt-preview,DavidGarciaCat/letsencrypt,bsmr-misc-forks/letsencrypt,lmcro/letsencrypt,DavidGarciaCat/letsencrypt,letsencrypt/letsencrypt,dietsche/letsencrypt,thanatos/lets-encrypt-preview,jsha/letsencrypt,dietsche/letsencrypt,mitnk/letsencrypt,stweil/letsencrypt,jtl999/certbot,jtl999/certbot,TheBoegl/letsencrypt,bsmr-misc-forks/letsencrypt,wteiken/letsencrypt,letsencrypt/letsencrypt