[CP-11175] Report presence of XenDesktop VDA on Guest into xenstore
[CP-11175] Report presence of XenDesktop VDA on Guest into xenstore

data/xd/present : 0 = not present, 1 = present
data/xd/product_installed : VDA ProductInstalled

Only set at start of day by the guest agent, not updated until
restarted (or resumed from suspend etc)

Signed-off-by: Ben Chalmers <b3747009c0bd3b0a8ac423a403e103e776512006@citrix.com>

xenserver/win-xenguestagent,kostaslamda/win-xenguestagent,kostaslamda/win-xenguestagent,xenserver/win-xenguestagent