Add old design doc for tunnelling

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
Merge pull request #2004 from robhoes/doctest

Add old design doc for tunnelling
And old design doc for GPU passthrough

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
Merge pull request #2005 from robhoes/doctest

And old design doc for GPU passthrough