Revisit the way frontend options are passed to the scheduler backends #75
Description
Currently, this is controlled by the sched_* arguments plus the sched_options. The problem with this approach is bugs like this. I think the best way to pass everything through sched_options or options and each back end should map specific properties to options. This is a rough idea, we should work on it a bit.
Internal issue: https://madra.cscs.ch/scs/reframe/issues/543