allow package managment in cloud-init by default

This enables the "yum-add-repo" and "package-update-upgrade-install"
modules in /etc/cloud.cfg, which permits people to install new yum
repositories and packages via the cloud-config mechanism:

    packages:
     - vim-enhanced
     - git

These are not enabled by default which can be confusing to people trying to install packages using the examples in the documentation.