Fix/2.2/pinstaged1

Fixes unit test regression introduced in 0eb17558d13723f5926dc5639ce1c8686bb2ba3d Since file size is required attribute it has to be specified


RB: https://rb.dcache.org/r/7057/
Acked-by: Paul Millar 
Target: 2.2 
Require-book: no 
Require-notes: no