cmd/jujud: rework upgrade tests
cmd/jujud: rework upgrade tests

Take advantage of extracted upgrade steps worker. The upgrade tests
are now significantly simpler and faster.

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