add tests exposing co_broadcast and co_reduce bugs

[everythingfunctional]

To demonstrate the presence of the bugs you can run the isolated tests with either:

GASNET_PSHM_NODES=2 ./build/run-fpm.sh test -- -f '(caffeinate|co_broadcast)' -f '(caffeinate|derived type)' -d

or

GASNET_PSHM_NODES=2 ./build/run-fpm.sh test -- -f '(caffeinate|co_reduce)' -f '(caffeinate|derived type)' -d

[bonachea]

Is there an open issue for these known defects?

If not, please open one with at least a minimal description of the failure.

On a related note, does our CI infrastructure have a way to mark "known failures"? If not, won't merging this result in CI failure for even unrelated PRs?

We should probably discuss our policy for how to handle known defects: specifically whether tests revealing a known failure should be committed pre-emptively with some kind of known failure indicator, or whether known defect reproducers should remain only in the issue tracker until there is a PR that repairs the defect and also adds a regression test for the fixed defect.

[everythingfunctional]

Yeah, totally wasn't expecting to merge this until we had a fix for each, but wanted to have concrete examples for discussion. I'll open an issue as well.