idempotent task updating /etc/sysconfig/network, testing with Ansible 1.9 and updated to ansible_distributions

ansible_distributions is generally more reliable for this purpose
the redirected echo was overwriting the network file and was not really needed. removed.
second task tackling the network file could be using the more elegant lineinfile module

Several conceptual improvements can be made and some other additions (i.e. debian playbook).

Would be nice to end up with a comprehensive and sufficient enough role to use as a proof that the 'hostname' module of Ansible should be doing most of these steps by itself :)