TLS support for VNC Websockets

Added TLS support to the VNC QEMU Websockets implementation.
VNC-TLS needs to be enabled for this feature to be used.

The required certificates are specified as in case of VNC-TLS
with the VNC parameter "x509=<path>".

If the server certificate isn't signed by a rooth authority it needs to
be manually imported in the browser because at least in case of Firefox
and Chrome there is no user dialog, the connection just gets canceled.

As a side note VEncrypt over Websocket doesn't work atm because TLS can't
be stacked in the current implementation. (It also didn't work before)
Nevertheless to my knowledge there is no HTML 5 VNC client which supports
it and the Websocket connection can be encrypted with regular TLS now so
it should be fine for most use cases.

Signed-off-by: Tim Hardeck <thardeck@suse.de>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
Message-id: 1366727581-5772-1-git-send-email-thardeck@suse.de
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>