Puppet parser function for frtch network information aboun network roles.

This function get get network config Hash, network_role name and mode -- and return information about network role.

ex: 
```ruby
get_network_role_property(network_config_hash, 'admin', 'interface')
```
You can use following modes:
      interface -- network interface for the network_role
      ipaddr -- IP address for the network_role
      cidr -- CIDR-notated IP addr and mask for the network_role
      netmask -- string, contains dotted nemmask
      ipaddr_netmask_pair -- list of ipaddr and netmask