libsubprocess: bulk-exec: fix bulk_exec_active_ranks()

Problem: bulk_exec_active_ranks() doesn't include subprocesses
that have exited, but are still waiting for output. This can cause
confusion since those ranks are still holding up completeion of the
bulk-exec operation.

Use flux_subprocess_active() instead of checking for the running
state to properly report active ranks and not just running ranks.

src/common/libsubprocess/bulk-exec.c

@@ -121,7 +121,7 @@ struct idset *bulk_exec_active_ranks (struct bulk_exec *exec)
 
     p = zlist_first (exec->processes);
     while (p) {
-        if (flux_subprocess_state (p) == FLUX_SUBPROCESS_RUNNING) {
+        if (flux_subprocess_active (p)) {
             int rank = flux_subprocess_rank (p);
             if (rank >= 0 && idset_set (ranks, rank) < 0) {
                 goto error;