Here's a simple patch that does what I had in mind. It allows providing for an arbitrary schedule file in both the check and installcheck recipes. The historic behaviour is preserved.
Hmm, installcheck command with SCHEDULE set as "Parallel" does not honor "MAXCONNOPT" settings in the attached patch.
And, now after your patch, do we still need "installcheck-parallel" command? It is redundant IMO, just give a thought.
Documentation changes("Running the Tests") are also required as the behavior documented is now changed in this patch.