CentOS 7 has a release of 7.0.1406

`os_release` in `utils/cobbler.py` fails on CentOS 7 as it cannot find a valid "float" in `/etc/redhat-release`.

    > rpm -qf /etc/redhat-release
    centos-release-7-0.1406.el7.centos.2.3.x86_64
    > cat /etc/redhat-release
    CentOS Linux release 7.0.1406 (Core)

This may also be cherry-picked in release26 as well.