change error message when ipv6 bridge config is present
change error message when ipv6 bridge config is present

Signed-off-by: Tycho Andersen <10c18fcb898ee6b17d6575d444b125d10b3f4d6a@canonical.com>

macgreagoir/juju,bac/juju,frankban/juju,dimitern/juju,dimitern/juju,alesstimec/juju,howbazaar/juju,gabriel-samfira/juju,alesstimec/juju,dimitern/juju,macgreagoir/juju,perrito666/juju,reedobrien/juju,howbazaar/juju,frankban/juju,AdamIsrael/juju,marcmolla/juju,perrito666/juju,bac/juju,reedobrien/juju,mjs/juju,marcmolla/juju,perrito666/juju,perrito666/juju,mjs/juju,ericsnowcurrently/juju,ericsnowcurrently/juju,macgreagoir/juju,mjs/juju,marcmolla/juju,frankban/juju,howbazaar/juju,macgreagoir/juju,dimitern/juju,waigani/juju,macgreagoir/juju,mjs/juju,anastasiamac/juju,gabriel-samfira/juju,waigani/juju,alesstimec/juju,waigani/juju,ericsnowcurrently/juju,mikemccracken/juju,mjs/juju,mikemccracken/juju,mjs/juju,AdamIsrael/juju,anastasiamac/juju,marcmolla/juju,anastasiamac/juju,anastasiamac/juju,alesstimec/juju,alesstimec/juju,gabriel-samfira/juju,ericsnowcurrently/juju,anastasiamac/juju,gabriel-samfira/juju,bac/juju,frankban/juju,ericsnowcurrently/juju,mikemccracken/juju,waigani/juju,bac/juju,reedobrien/juju,dimitern/juju,gabriel-samfira/juju,AdamIsrael/juju,AdamIsrael/juju,mikemccracken/juju,mjs/juju,reedobrien/juju,reedobrien/juju,bac/juju,marcmolla/juju,perrito666/juju,frankban/juju,mikemccracken/juju,howbazaar/juju,howbazaar/juju