As mentioned in a comment (which this patch deletes), calling this
class 'Raw' was confusing, because it is not always raw. It is also a
source of bugs, because some code assumes that the format is always
raw, which it is not. This patch does not fix those bugs.
We rename it to 'Flat', which describes it accurately. We also add
doctext describing what it does.
DocImpact
The config option libvirt.images_type gets an additional value:
'flat'. The effect of this is identical to setting the value 'raw'.
Change-Id: I93f0a2cc568b60c2b3f7509449167f03c3f30fb5
cff4d78a4a