[r=jameinel],[bug=1253631] cmd/juju/addmachine.go: first part of compat
[r=jameinel],[bug=1253631] cmd/juju/addmachine.go: first part of compat

This handles the part of add-machine that doesn't involve manual
provisioning. It makes trunk compatible with 1.16.3 for a simple
"juju add-machine" or "juju add-machine lxc". The manual provisioning
case has a bunch more code, so that will be a followup patch.

https://codereview.appspot.com/34890044/
frankban/juju-tmp,dooferlad/juju,AdamIsrael/juju,bogdanteleaga/juju,AdamIsrael/juju,reedobrien/juju,kat-co/juju,bogdanteleaga/juju,makyo/juju,fwereade/juju,frankban/juju,kat-co/juju,thomnico/juju,ericsnowcurrently/juju,bac/juju,frankban/juju,gabriel-samfira/juju,howbazaar/juju,Altoros/juju-cloudsigma,dooferlad/juju,cmars/juju,mjs/juju,alesstimec/juju,reedobrien/juju,jrwren/juju,bac/juju,mikemccracken/juju,axw/juju,cmars/juju,mjs/juju,davecheney/juju,mikemccracken/juju,tych0/juju,ericsnowcurrently/juju,tych0/juju,frobware/juju,tych0/juju,frankban/juju,mhilton/juju-juju,davecheney/juju,makyo/juju,macgreagoir/juju,voidspace/juju,gabriel-samfira/juju,frobware/juju,thomnico/juju,howbazaar/juju,fwereade/juju,cherylj/juju,reedobrien/store,howbazaar/juju,alesstimec/juju,anastasiamac/juju,dimitern/juju,macgreagoir/juju,frankban/juju-tmp,marcmolla/juju,bz2/juju,mjs/juju,reedobrien/juju,anastasiamac/juju,gabriel-samfira/juju,waigani/juju,ericsnowcurrently/juju,mjs/juju,tsakas/juju,axw/juju,mhilton/juju-juju,mikemccracken/juju,gabriel-samfira/juju,marcmolla/juju,bac/juju,rogpeppe/juju,marcoceppi/juju,voidspace/juju,reedobrien/juju,bz2/juju,frankban/juju,sinzui/juju,ericsnowcurrently/juju,AdamIsrael/juju,kat-co/juju,cloud-green/juju,tasdomas/juju,kat-co/juju,mjs/juju,bac/juju,rogpeppe/juju,davecheney/juju,marcmolla/juju,dimitern/juju,mhilton/juju,mhilton/juju-juju,mikemccracken/juju,dimitern/juju,cloud-green/juju,anastasiamac/juju,anastasiamac/juju,frankban/juju-tmp,ericsnowcurrently/juju,macgreagoir/juju,mhilton/juju,wwitzel3/juju,perrito666/juju,cloud-green/juju,cmars/juju,makyo/juju,mjs/juju,macgreagoir/juju,mattyw/juju,cherylj/juju,Altoros/juju-vmware,mhilton/juju-juju,mjs/juju,dooferlad/juju,jrwren/juju,tasdomas/juju,bz2/juju,anastasiamac/juju,axw/juju,cherylj/juju,kat-co/juju,Altoros/juju-vmware,bogdanteleaga/juju,thomnico/juju,perrito666/juju,tsakas/juju,Altoros/juju-cloudsigma,waigani/juju,AdamIsrael/juju,macgreagoir/juju,Altoros/juju-cloudsigma,frankban/juju,cloud-green/juju,fwereade/juju,howbazaar/juju,frankban/juju-tmp,makyo/juju,howbazaar/juju,mattyw/juju,tych0/juju,Altoros/juju-vmware,tsakas/juju,mattyw/juju,cherylj/juju,frobware/juju,mhilton/juju,wwitzel3/juju,dimitern/juju,marcoceppi/juju,sinzui/juju,bac/juju,wwitzel3/juju,perrito666/juju,Altoros/juju-cloudsigma,waigani/juju,marcmolla/juju,reedobrien/juju,bogdanteleaga/juju,alesstimec/juju,tsakas/juju,fwereade/juju,dimitern/juju,alesstimec/juju,dooferlad/juju,alesstimec/juju,marcmolla/juju,perrito666/juju,sinzui/juju,sinzui/juju,thomnico/juju,dooferlad/juju,mikemccracken/juju,perrito666/juju,axw/juju,davecheney/juju,bz2/juju,tasdomas/juju,voidspace/juju,gabriel-samfira/juju,wwitzel3/juju,tasdomas/juju,marcoceppi/juju,jrwren/juju,mattyw/juju,Altoros/juju-vmware,voidspace/juju,axw/juju,mhilton/juju,waigani/juju,marcoceppi/juju,rogpeppe/juju,bz2/juju,cmars/juju