srun: disable srun on local/remote Cray systems

This disables srun support:
 * on native Cray systems (having 'apbasil' available) it is currently
   not possible, since it would require to have a slurmd on each compute
   node -- which at least at the moment is still done by the ALPS daemons;
 * if running srun from a remote host and trying to launch a job on a remote
   Cray host, the same consideration applies;
 * trying to use Cray-enabled srun (HAVE_CRAY) to launch a job on a non-Cray
   system is allowed to proceed.srun: disable srun on local/remote Cray systems

14_srun.diff