When troubleshooting download issues, which may present
as checksum validation failures, it is difficult to understand
if the *entire* file was downloaded due to the way HTTP works.
In that, a download may start with a successful result code,
and the content is streamed out until the socket is closed.
But with HTTP there is no way to know if that socket closed
prematurely and the original server size is *also* an optional
field, so just log the size we got to so we don't drive the
humans [more-]insane.
Also now logs the (optional) content-length field if
supplied by the server.
Change-Id: Id71b167f4e330d54b9afddf95f1a2ef9e40398bf
c65ad42ff1