This used to get all the interfaces and ssids when the completions
were loaded. That's obviously wrong, given that ssids especially can, you know, change
These printed an error on load if networkmanager isn't running.
Since at that point it's not useful to complete anything, just try the
first call and if that fails exit.
Set variables for available connections and SSIDs only when the completion is loaded.
This is not perfect but faster than scanning for connections everytime.
Don't complete connection UUID, DBUS-PATH, ACTIVE-PATH because they are unintelligible.
Instead only complete the connection name.
See #6379
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