cobblerd cannot start on CentOS 7

CentOS has a release of 7.0.1406, which is not a "float".

Use only the first two digits when assuming it is a float.

> 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)