When a user does not define the image size for a compose the default
image size of that image type is used. In order to properly store the
compose's image size even if the default is used the store calls the
distro function GetSizeForOutputType. This function accepts an output
format and image size. If the image size is 0 then the default
value for the output format will be returned. Also, for vhd images the
size must be rounded. This is now handled in the distro function instead
of the api.
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