pool: Preserve HSM option ordering

Although the script should not care about the order, it might. Also,
it is nicer to see the options in the order you put them rather than
how they got hashed.

Target: trunk
Request: 2.11
Request: 2.10
Request: 2.9
Require-notes: yes
Require-book: no
Acked-by: Christian Bernardt <christian.bernardt@desy.de>
Patch: https://rb.dcache.org/r/7621/