HPCC-12111 Use a different sub directory for each slave instance

Use a sub directory based on port number under the configured
main temp directory, to keep temp files separate from different
slaves separately. This is mainly so that on restart, a slave
can clear out it's own temps easily.

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #6360 from jakesmith/hpcc-12111

HPCC-12111 Use a different sub directory for each slave instance

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>