Fix some minor issues

- Script should be /bin/bash in case one wants it to be able to use the module system inside
- Must create the directory elbencho doesn't
- One should wait for the background processes before exiting the script

storage-benchmark.sbatch

-#!/bin/sh
+#!/bin/bash
 #SBATCH -J arrh-storage-benchmark
 
 usage() {
@@ -34,6 +34,8 @@ if [ -z "$DIRECTORY" ]
 then usage
 fi
 
+mkdir -p $DIRECTORY
+
 NNODES=$SLURM_NNODES
 THREADS=$SLURM_CPUS_PER_TASK
 HOSTS=$(scontrol show hostnames | tr '\n' ',')
@@ -81,3 +83,5 @@ echo
 info "Benchmark done"
 
 elbencho --hosts "$HOSTS" --quit
+
+wait