scontrol: disable wait_job on Cray systems

On Cray, wait_job means to confirm the already existing ALPS reservation. This
is handled already:
 * for salloc by select_g_job_ready() - hence no need to call again;
 * for batch jobs it is done in the stepdmanager.
Hence just print a warning to the user.

13_scontrol-no-wait_job.diff