Set the correct mpirun_command to go with the localhost computer for the AiiDA install

[sphuber]

The localhost computer is configured to use the SLURM scheduler but the mpirun_command uses mpirun instead of srun. Fixing this is blocked by the following PR for the AiiDA ansible role: marvel-nccr/ansible-role-aiida#69

[ltalirz]

I'm not sure that is really necessary, see https://www.open-mpi.org/faq/?category=slurm

[sphuber]

This came during a discussion on an issue for aiida-common-workflows where a CP2K run wasn't running properly in parallel. The suspicion was raised that it might had to do with using mpirun instead of srun, but it seems indeed that this is not necessarily required. Fine to close this issue for now.