worker/peergrouper: avoid unnecessary replicaset initiate attempts
worker/peergrouper: avoid unnecessary replicaset initiate attempts

InitiateMongoServer kept trying to initiate the replicaset when it was
already initiated. The retry loop is now exited early if the
replicaset is already up.

This also reduces the peergrouper tests run time from ~2 mins to a few
seconds!

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