Add enablement for cloud-init in centos
Add enablement for cloud-init in centos

  * Enable cloud-init
    - Install cloud-init from github's RPM
    - Install dmidecode
    - Disable systemd units now taken care of by cloud-init
    - Override cloud-init root disablement to keep backward compatibility
    - Remove masking of sshd-keygen.service now needed by cloud-init

scaleway/image-centos