Fix t/rose-mpi-launch --inner: use numeric ulimit

Previously it uses `ulimit -s unlimited`. Some sites do not like this. A
numeric value based on half the site limit should work better for them.
Update CHANGES.md
Merge pull request #1098 from matthewrmshin/fix-t-mpi-launch-unlimit-s

Fix t/rose-mpi-launch --inner: use numeric ulimit
Update CONTRIBUTING.md

Added myself to the list