provider/ec2: fix map ordering bug in test
provider/ec2: fix map ordering bug in test

ec2.Volumes() does not return in a defined order.

Fixes https://bugs.launchpad.net/juju-core/+bug/1479024

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