Run steps: ordering support and streaming stdout

Runs with something like this:

$ cat config-run 
[RUN-STEP-A]
run_rank=1
run_order=pre
run_type=workload
run_cmd=sleep 1
call_type=local
[RUN-STEP-B]
run_rank=2
run_order=pre
run_type=workload
run_cmd=sleep 2
call_type=local
[RUN-STEP-C]
run_rank=3
run_type=workload
run_cmd=sleep 3
call_type=local