Empty lines in built job scripts

[teojgo]

For example for the petsc example the job script contains the following:

#!/bin/bash -l
#SBATCH --job-name="rfm_PetscPoisson2DCheck_dynamic_job"
#SBATCH --time=0:10:0
#SBATCH --ntasks=16
#SBATCH --ntasks-per-node=8








#SBATCH --output=/users/manitart/reframe_dev_public/stage/dom/gpu/PrgEnv-cray/PetscPoisson2DCheck_dynamic/rfm_PetscPoisson2DCheck_dynamic_job.out
#SBATCH --error=/users/manitart/reframe_dev_public/stage/dom/gpu/PrgEnv-cray/PetscPoisson2DCheck_dynamic/rfm_PetscPoisson2DCheck_dynamic_job.err

#SBATCH --constraint=gpu
module load daint-gpu
module load PrgEnv-cray
module load cray-petsc
srun ./PetscPoisson2DCheck_dynamic -da_grid_x 4 -da_grid_y 4 -ksp_monitor

This seems to have been introduced by #340 since in the finalize method of ShellScriptGenerator when joining \n with a list that contain empty strings, empty lines are introduced.