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