G5k: Generate the network id automatically if none is passed
Instead of doing this:
network = G5kNetworkConf(
id="n1", type="prod", roles=["my_network"], site="rennes"
)
We'd like to do:
network = G5kNetworkConf(
type="prod", roles=["my_network"], site="rennes"
)
The id would be generated automatically.