Code review comment for lp:~blake-rouse/maas/commissioning-get-disk-info

This looks generally good. I've got a bunch of comments but more importantly, I'm wondering about the failure modes for this. See below.

This uses a lot of commands and a fair share of parsing. All of which could go wrong at some point and break the commissioning. I think it's worth taking a step back and thinking about the failure modes here:
- which part of the code are likely to fail (command failure, parsing failure, etc)? Can we make this more robust against non-fatal error?
- what's the failure mode? In other words, what is going to happen when this fails, what will the consequences be, how easy will it be to the user to get information about what's wrong?

What do you think?