apiserver: refactored upgradingRoot method check
apiserver: refactored upgradingRoot method check

Given that the API methods allowed during upgrade are all on the
Client facade, avoid having to write "Client." at the front of each
method name.

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