Do not use "wait -n" in order to support bash versions older than 5.0. (#1801)
Do not use "wait -n" in order to support bash versions older than 5.0. (#1801)

The single node launcher introduced by PR #1724 uses "wait -n". The "-n" flag was introduced in bash v5. This PR rewrites that piece of code to not use said flag.

Fixes #1797


Co-authored-by: Ben Clifford <6e9c823d93e7dad5e7e2198704c60762764c20c1@hawaga.org.uk>
Parsl/parsl,Parsl/parsl,Parsl/parsl,Parsl/parsl