libxl: cdrom eject and insert: write to /libxl

libxl: cdrom eject and insert: write to /libxl

Copy the new type and params values to /libxl, so that the information
in /libxl is kept up to date.

This is needed so that we can return this trustworthy information,
rather than trusting the backend-writeable parts of xenstore.

This is part of XSA-178.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>