srm: Clean up srmCopy request handling

Mostly cosmetic to mirror the other request implementations.
The bulk of the copy logic is unchanged and needs to be cleaned
up in a future patch.

Target: trunk
Require-notes: no
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: http://rb.dcache.org/r/6145/