rose mpi-launch: fix script exit syntax

The on-error `return` statements under `--inner` do not work under
`bash` and may confuse users into thinking that there may be some other
problems. This change should allow errors to be reported with less
confusion.
Merge pull request #1075 from matthewrmshin/fix-rose-mpi-launch-return

rose mpi-launch: fix script exit syntax
Merge branch 'master' into doc-suite-control
Doc: add chapter on utilities for suite control

More corrections following review.