It may not be possible to know in advance the total
size of image data which is to be uploaded, for example
if the data is being piped to stdin.
To handle this we use HTTP Transfer-Encoding: chunked
and do not set any image size headers.
Various subtly different cases needed to be handled for
both image-create and image-update, including:
* input from named pipe
* piped input of zero size
* regular file of zero length
Fix for bug 1056220.
Change-Id: I0c7f0a64d883e058993b954a1c465c5b057f2bcf
727aadbc25