listVolumes pool id

[Marcus Sorensen]

I almost can't believe this doesn't already exist, but I noticed that
listing a volume doesn't show you the id of the storage pool the
volume belongs to. It shows the pool name, but it seems that doesn't
have to be unique.  Does anyone have a problem with me adding that to
the listVolumes response?  Are there any tests that might fail due to
hardcoded response expectations?