Fix bug #1253625, compat with 1.16 for 'juju set/get-environment'
Fix bug #1253625, compat with 1.16 for 'juju set/get-environment'

In 1.17 we added EnvironmentSet and EnvironmentGet but those aren't
available in a 1.16 API server. So we fall back to direct DB access.

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