Add option to only configure repository

[blarghmatey]

Description of Issue/Question

It would be nice to be able to use the bootstrap script to set up the appropriate package repository for the given distribution without having to install the salt-minion or other packages. The use case here being that I would like to use the bootstrap script to populate the package repo using the runcmd stage of cloud-init and then use the salt-minion module subsequently to handle installing the minion package and populate the config and minion keys. When using the bootstrap script to install the minion it automatically generates keys which then fail to be accepted, vs the already accepted keys that I am passing to the salt-minion cloud-init module.