ui: add tracing of VNC operations related to QIOChannel

Trace anything which opens/closes/wraps a QIOChannel in the
VNC server.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170921121528.23935-2-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>