cmd/jujud: ensure we don't ensureMongoServer twice
cmd/jujud: ensure we don't ensureMongoServer twice

The upgrade-steps and StateWorker both call ensureMongoServer,
which is meant to check/set a flag so that we only set it up
once. There's an early exit case which meant that the flag was
not being set, which led to the upgrade-steps code restarting
mongo half-way through.

Fixes https://bugs.launchpad.net/juju-core/+bug/1338511

wwitzel3/juju,AdamIsrael/juju,bz2/juju,marcmolla/juju,alesstimec/juju,perrito666/juju,fwereade/juju,perrito666/juju,marcmolla/juju,tasdomas/juju,dimitern/juju,bac/juju,davecheney/juju,voidspace/juju,mhilton/juju-juju,voidspace/juju,reedobrien/juju,voidspace/juju,jrwren/juju,perrito666/juju,fwereade/juju,macgreagoir/juju,bz2/juju,alesstimec/juju,tsakas/juju,makyo/juju,bz2/juju,mjs/juju,anastasiamac/juju,cloud-green/juju,alesstimec/juju,ericsnowcurrently/juju,marcoceppi/juju,alesstimec/juju,Altoros/juju-cloudsigma,dimitern/juju,reedobrien/juju,sinzui/juju,kat-co/juju,macgreagoir/juju,bac/juju,mhilton/juju,howbazaar/juju,Altoros/juju-vmware,jrwren/juju,cloud-green/juju,reedobrien/juju,mjs/juju,mjs/juju,thomnico/juju,mjs/juju,waigani/juju,wwitzel3/juju,anastasiamac/juju,gabriel-samfira/juju,ericsnowcurrently/juju,tasdomas/juju,perrito666/juju,anastasiamac/juju,sinzui/juju,bogdanteleaga/juju,bogdanteleaga/juju,bac/juju,cmars/juju,tych0/juju,thomnico/juju,kat-co/juju,bogdanteleaga/juju,tasdomas/juju,mikemccracken/juju,gabriel-samfira/juju,marcmolla/juju,mhilton/juju-juju,frankban/juju-tmp,fwereade/juju,Altoros/juju-vmware,dimitern/juju,axw/juju,mhilton/juju,jrwren/juju,alesstimec/juju,dooferlad/juju,frankban/juju,cloud-green/juju,bac/juju,marcoceppi/juju,cmars/juju,mikemccracken/juju,axw/juju,cherylj/juju,axw/juju,frankban/juju-tmp,waigani/juju,tsakas/juju,reedobrien/juju,dooferlad/juju,gabriel-samfira/juju,AdamIsrael/juju,dooferlad/juju,davecheney/juju,axw/juju,waigani/juju,fwereade/juju,waigani/juju,ericsnowcurrently/juju,bz2/juju,gabriel-samfira/juju,Altoros/juju-cloudsigma,AdamIsrael/juju,makyo/juju,marcoceppi/juju,thomnico/juju,tsakas/juju,dimitern/juju,thomnico/juju,marcmolla/juju,Altoros/juju-vmware,makyo/juju,davecheney/juju,dooferlad/juju,cherylj/juju,voidspace/juju,perrito666/juju,mjs/juju,anastasiamac/juju,cloud-green/juju,kat-co/juju,axw/juju,cmars/juju,mhilton/juju-juju,frankban/juju,Altoros/juju-cloudsigma,mjs/juju,dooferlad/juju,howbazaar/juju,mikemccracken/juju,cherylj/juju,Altoros/juju-cloudsigma,anastasiamac/juju,kat-co/juju,tsakas/juju,bogdanteleaga/juju,wwitzel3/juju,frankban/juju,marcoceppi/juju,frankban/juju-tmp,kat-co/juju,ericsnowcurrently/juju,makyo/juju,mikemccracken/juju,mikemccracken/juju,macgreagoir/juju,Altoros/juju-vmware,howbazaar/juju,sinzui/juju,frankban/juju-tmp,tych0/juju,wwitzel3/juju,tych0/juju,tych0/juju,tasdomas/juju,howbazaar/juju,macgreagoir/juju,bz2/juju,marcmolla/juju,howbazaar/juju,bac/juju,mhilton/juju,AdamIsrael/juju,frankban/juju,cherylj/juju,ericsnowcurrently/juju,mjs/juju,reedobrien/juju,mhilton/juju,macgreagoir/juju,sinzui/juju,dimitern/juju,frankban/juju,davecheney/juju,mhilton/juju-juju,cmars/juju,gabriel-samfira/juju