Code review comment for lp://qastaging/~qzhang/lava-dispatcher/fix-867858

Hi Spring, a couple of problems here still.

1. I don't think we need to format the partitions twice.
2. There's still a window of opportunity where we could fail earlier before the formatting takes place. For instance, if the network fails to come up. I would suggest moving the formatting into a _format_foo() method, call the logging bit to give info that we are formatting, and call it very very early in run().