tools/xenstore: create_node: Don't defer work to undo any changes on failure

tools/xenstore: create_node: Don't defer work to undo any changes on failure

XSA-115 extended destroy_node() to update the node accounting for the
connection. The implementation is assuming the connection is the parent
of the node, however all the nodes are allocated using a separate context
(see process_message()). This will result to crash (or corrupt) xenstored
as the pointer is wrongly used.

In case of an error, any changes to the database or update to the
accounting will now be reverted in create_node() by calling directly
destroy_node(). This has the nice advantage to remove the loop to unset
the destructors in case of success.

Take the opportunity to free the nodes right now as they are not
going to be reachable (the function returns NULL) and are just wasting
resources.

This is XSA-414 / CVE-2022-42309.

Fixes: 0bfb2101f243 ("tools/xenstore: fix node accounting after failed node creation")
Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Juergen Gross <jgross@suse.com>