[r=rogpeppe] provider/ec2: use s3.RetryAttempts
[r=rogpeppe] provider/ec2: use s3.RetryAttempts

This speeds the tests up from about 80s to 3s.

I've also taken this opportunity to clean up some
of the test code.

https://codereview.appspot.com/12787050/
makyo/juju,tych0/juju,wwitzel3/juju,marcoceppi/juju,kat-co/juju,sinzui/juju,dooferlad/juju,cmars/juju,mhilton/juju,mattyw/juju,davecheney/juju,macgreagoir/juju,mjs/juju,frankban/juju,axw/juju,axw/juju,tsakas/juju,tasdomas/juju,axw/juju,howbazaar/juju,sinzui/juju,tych0/juju,rogpeppe/juju,bz2/juju,rogpeppe/juju,perrito666/juju,frankban/juju,kat-co/juju,Altoros/juju-vmware,bz2/juju,davecheney/juju,dimitern/juju,kat-co/juju,thomnico/juju,reedobrien/juju,reedobrien/juju,bac/juju,alesstimec/juju,davecheney/juju,alesstimec/juju,marcoceppi/juju,tasdomas/juju,bz2/juju,howbazaar/juju,gabriel-samfira/juju,howbazaar/juju,anastasiamac/juju,rogpeppe/juju,wwitzel3/juju,perrito666/juju,anastasiamac/juju,macgreagoir/juju,AdamIsrael/juju,ericsnowcurrently/juju,gabriel-samfira/juju,macgreagoir/juju,voidspace/juju,davecheney/juju,dimitern/juju,mikemccracken/juju,frobware/juju,Altoros/juju-cloudsigma,ericsnowcurrently/juju,marcmolla/juju,cmars/juju,AdamIsrael/juju,mjs/juju,voidspace/juju,waigani/juju,frankban/juju,frobware/juju,fwereade/juju,Altoros/juju-cloudsigma,mhilton/juju,frankban/juju,howbazaar/juju,mhilton/juju,makyo/juju,cherylj/juju,waigani/juju,frobware/juju,wwitzel3/juju,cmars/juju,cherylj/juju,mhilton/juju,mikemccracken/juju,mikemccracken/juju,tsakas/juju,frankban/juju-tmp,dooferlad/juju,mikemccracken/juju,macgreagoir/juju,bac/juju,bz2/juju,cloud-green/juju,mattyw/juju,tych0/juju,axw/juju,mjs/juju,waigani/juju,alesstimec/juju,mhilton/juju-juju,cloud-green/juju,cloud-green/juju,macgreagoir/juju,howbazaar/juju,AdamIsrael/juju,bogdanteleaga/juju,voidspace/juju,makyo/juju,frankban/juju,Altoros/juju-vmware,tasdomas/juju,anastasiamac/juju,jrwren/juju,cherylj/juju,alesstimec/juju,mattyw/juju,AdamIsrael/juju,anastasiamac/juju,frankban/juju-tmp,perrito666/juju,wwitzel3/juju,mhilton/juju-juju,marcmolla/juju,waigani/juju,marcmolla/juju,tych0/juju,mjs/juju,bac/juju,perrito666/juju,anastasiamac/juju,cmars/juju,thomnico/juju,dimitern/juju,gabriel-samfira/juju,ericsnowcurrently/juju,reedobrien/juju,tasdomas/juju,tsakas/juju,ericsnowcurrently/juju,dooferlad/juju,bz2/juju,kat-co/juju,mjs/juju,mjs/juju,mjs/juju,makyo/juju,cloud-green/juju,mhilton/juju-juju,frankban/juju-tmp,jrwren/juju,dimitern/juju,bogdanteleaga/juju,sinzui/juju,ericsnowcurrently/juju,reedobrien/juju,mikemccracken/juju,alesstimec/juju,fwereade/juju,voidspace/juju,bac/juju,axw/juju,marcoceppi/juju,marcmolla/juju,Altoros/juju-vmware,reedobrien/juju,kat-co/juju,tsakas/juju,Altoros/juju-cloudsigma,fwereade/juju,thomnico/juju,marcoceppi/juju,Altoros/juju-vmware,perrito666/juju,dooferlad/juju,marcmolla/juju,mhilton/juju-juju,jrwren/juju,frankban/juju-tmp,bogdanteleaga/juju,dimitern/juju,sinzui/juju,fwereade/juju,cherylj/juju,gabriel-samfira/juju,Altoros/juju-cloudsigma,mattyw/juju,dooferlad/juju,reedobrien/store,bogdanteleaga/juju,thomnico/juju,gabriel-samfira/juju,bac/juju