Function to list network namespaces

[zeffron]

It would be very helpful to have a function that's an equivalent to ip netns list. The use case is for things like Telegraf which gather metrics and monitor system status. System administrators may want to gather metrics from all namespaces, but may not know what the namespaces are going to be ahead of time.

[zeffron]

Ideally, the function would list all of the network namespaces on the system, though, and not just those created with ip (or otherwise listed in /var/run/netns