This workaround stage prevents srun from returning 0 to the upper stages
when a signal happens after MPI_Finalize. It writes the return code to a
file named .srun.rc.$rank and later checks that exists and contains a 0.
When the program is killed, exits with non-zero and the error is
propagated to the baywatch stage, which aborts immediately without
creating the rc file.
These targets allow one experiment to directly refer to another
experiment results, thus a dependency chain can be formed to ensure
execution order.
It also simplifies the dataset definition, as they can be automatically
fetched from the experiment directly.
Now the options cpusPerTask ntasksPerNode nodes and jobName are required
for the sbatch stage. Also cpuBind has been removed and is always set to
"cores,verbose" in the srun stage.
The bsc attrset is now extensible: replacing a few bsc packages is very
fast. Also we allow the complete bscpkgs to be within other custom
overlays (not tested yet).
