vfs_fruit: prepare fruit_pwrite_meta() for on-demand opening and writing

vfs_fruit: prepare fruit_pwrite_meta() for on-demand opening and writing

This avoid creating files or blobs in our streams backend when a client
creates a stream but hasn't written anything yet. This is the only sane
way to implement the following semantics:

* client 1: create stream "file:foo"

* client 2: open stream "file:foo"

The second operation of client 2 must fail with NT_STATUS_NOT_FOUND.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13646

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>