Update Git Repo for rpm-ostree-toolbox

The following changes help make rpm-ostree-toolbox be able work
with this git repository.  With -toolbox, you can create custom
atomic trees, disk images, and installer media.

    * CentOS-Base.repo
        - toolbox can only handle one repo description per file

    * CentOS-updates.repo
        - Addition of the updates repo

    * centos-7.tdl
        - generic centos7 TDL for building a utility image

    * centos-atomic-base.json
        - Added updates repo
        - corrected error for missing comma in repos list
        - remove extlinux, use grub2

    * centos-atomic-cloud-docker-host.json
        - renamed to centos-atomic-host.json which -toolbox will
          automatically detect.

    * centos-atomic-host-7.ks
        - kickstart needed by imagefactory during disk creations

    * centos-atomic-host-7.tdl
        - atomic TDL file needed by imagefactory during disk creations

    * config.ini
        - main control file needed for rpm-ostree-toolbox operations
Adding new CentOS anaconda URL and -extras repo