Use HTTPS for qemu.org and other domains

qemu.org enabled HTTPS in 2017 and it should be used instead of HTTP.
There are also URLs to json.org, openvpn.net, and other domains that
support HTTPS.

This patch updates the qemu.org domains everywhere and also third-party
domains that I have checked.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20171121120435.28728-3-stefanha@redhat.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>