If running as normal user, chown will fail. This isn't a problem,
because the file is probably already owned by the correct user. The
whole point about this chown is to give access to the file for normal
user, so if the write succeeded, it isn't needed.
HVM can set some xenstore entries (in qubes-tools/ subtree) to pass
informations about installed tools to dom0. qubes.NotifyTools service
triggers update of VM properties (like qrexec_installed).
This way, after installation of Qubes Windows Tools, the user doesn't need
to change any VM settings to use the tools.
