get_attr output attribute is always set to private

By default the private network is named 'private' and that's how heat-translator translates to produce output with get_attr function in the translated template: e.g.
get_attr: [my_instance, networks, private, 0]
This mapping happens for TOSCA Compute's private_address attribute.
However if user has a private network with a name that's not 'private' then translated template won't produce any output because there is no 'private' named network.
The solution could be to programmatically find private network name an instance is associated with or ask user to provide the name of network as input to the translator.