Fixed ERB template deprecation warnings

In recent Puppet versions, ERB templates give deprecation warnings, e.g.

    Warning: Variable access via 'interface' is deprecated. Use '@interface' instead. template[/tmp/vagrant-puppet/modules-0/network/templates/ifcfg-eth.erb]:4
       (at /tmp/vagrant-puppet/modules-0/network/templates/ifcfg-eth.erb:4:in `result')

These are now fixed