environs/cloudinit: prealloc smaller journal files
environs/cloudinit: prealloc smaller journal files

Prealloc 1M journal files upfront, to prevent mongo from doing
that and allocating 100M+ files which take a while to be created.

Let's keep an eye on the effects this will have in practice in
the form of slow-downs while the database itself has to allocate
the next file.

R=fwereade
CC=
https://codereview.appspot.com/6569060

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