tools/xenstore: dump the xenstore state for live update

tools/xenstore: dump the xenstore state for live update

Dump the complete Xenstore status to a file (daemon case) or memory
(stubdom case).

As we don't know the exact length of the needed area in advance we are
using an anonymous rather large mapping in stubdom case, which will
use only virtual address space until accessed. And as we are writing
the area in a sequential manner this is fine. As the initial size we
are choosing the double size of the memory allocated via talloc(),
which should be more than enough.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Paul Durrant <paul@xen.org>
Acked-by: Julien Grall <jgrall@amazon.com>
Acked-by: Wei Liu <wl@xen.org>