Write updates.tsv
Write updates.tsv

Adds new environment variable "UPDATE_URL" as the base url of updates,
or defaults to an obvious wrong location. Writes the managementagent
msi's details on a tab seperated file containing url, version, size,
arch to installer folder/tar file

Signed-off-by: Owen Smith <ff5e3d9c9f82290ce2a1ee2b399fd0e8322eba85@citrix.com>

xenserver/win-installer,kostaslamda/win-installer,benchalmers/win-installer,OwenSmith/win-installer,xenserver/win-installer,OwenSmith/win-installer,xenserver/win-installer,OwenSmith/win-installer,kostaslamda/win-installer,xenserver/win-installer,OwenSmith/win-installer,kostaslamda/win-installer,benchalmers/win-installer,kostaslamda/win-installer,benchalmers/win-installer,OwenSmith/win-installer,benchalmers/win-installer,benchalmers/win-installer,xenserver/win-installer,kostaslamda/win-installer