--enablerepo/--disablerepo flag now works

the --enablerepo flag didn't work because you init the repo as s3 repos before the --enablerepo flagged is processed. By changing the order of operations where s3 repos are initiated from init_hook to prereposetup_hook,  the s3 repos are init after the command line arguments are processed.

Also removed a workaround that I implemented a while ago. The 'enabled' attr in a yum config file wasn't being taken into affect, and I added a couple lines so it would. I didn't know at the time that there already is a method to get if the repo is enabled in the config file or not.