Code review comment for lp:~harlowja/cloud-init/ds-reset-fix

I'm calling this "merged" at revno 747 that I just pushed.
I picked the fetch_base_config() method out but did not take the other changes.

The request for this review came because I had missed some function when backporting something to quantal, and was seeing something I thought was related (that a 'cloud' passed to a config did not have a distro).

That was fixed by pulling in revno 720 and 722 though.