WIP: templates/online_pe.jinja2: Specify the path to mpirun in uploaded parameter...

Currently lalinference_mcmc fails complaining that it can not find mpirun due to https://git.ligo.org/sccb/requests/issues/210. For online runs, we can solve this issue by running touch ~/.useintel_2018u3 in the emfollow machine. On the other hand, for manual runs, it is difficult to ensure that all of the ROTA people run the above command. Therefore, we hardcode the path to mpirun instead in the uploaded ini file.

cc: @vivien @leo-singer