Fix handling of HTTP 1.0 responses with Connection: Keep-Alive

Fix handling of HTTP 1.0 responses with Connection: Keep-Alive

An HTTP 1.0 response can keepalive and have a Connection-Length: header,
and this is seen in some cases with the initial redirect when we connect
to a VPN server (Red Hat bug #553817). Fix and clean up the response
handling code accordingly.

I _really_ wish I didn't have to write my own HTTP code, and that one of
the available libraries was actually able to support SSL connections
with a certificate from a TPM.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>