util.mount_cb only supports passing through a single (positional) argument to the wrapped function

[Dan Watkins]

This makes it difficult to use with a function that needs to take more than a single positional parameter, or any keyword arguments; you have to partially apply the function before calling mount_cb.

I propose adding `args` and `kwargs` parameters, which will be passed to the callback function using *args and **kwargs. (For bonus points, refactor all current callsites to pass `args` so we can drop the `data` argument entirely.)

[Dan Watkins (oddbloke)]

I haven't started work on this specific feature, but I have started looking at writing tests for mount_cb's current behaviour as it is presently untested.

[Dan Watkins (oddbloke)]

That testing is now up at https://github.com/canonical/cloud-init/pull/463

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/3751