scripts: fix java invocation

Patch https://rb.dcache.org/r/7168/ committed as 8ea811d5 prevents
dCache from starting as the 'pool.dcap.port' is now marked
forbidden yet the patch failed to update the reference to this
property in the dCache command-line.

This patch fixes the command-line to use the updated property name.

Target: master
Patch: https://rb.dcache.org/r/7271/
Acked-by: Gerd Behrmann
Requires-book: no
Requires-notes: no