CP-8987: Add domain's Xenstore tree to the Xenops suspend record

Add everything under /local/domain/<domid>/ to the suspend image as part of the
Xenops metadata record.

This has been done so that it serialises in a way that can be deserialised
with the upstream xenopsd (using sexplib).

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
CP-8987: Don't log Xenops suspend image record contents

It is too large to log when reading and writing but will be of use when
inspecing a suspend image.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>