HTTP: handle `Connection:close`
HTTP: handle `Connection:close`

If the HTTP server responds with `Connection:close` then we

- must copy any response body that might be present, even if we have
  no further information about it (e.g. no `Transfer-encoding` or
  `Content-length` headers)
- must actually close the connection

This mostly affects the transparent proxy which has to cope with
HTTP/1.0 traffic. The explicitly-proxied traffic is all HTTP/1.1
and includes the extra headers.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@docker.com>

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit