Convert job script into Python and put it in `runcirrus`

[pinkwah]

Instead of creating a job script which uses bash, instead internalise it in Python. The runcirrus script exists and is the same both on TGX and LSF cluster, so we can reuse it.

1. User writes runcirrus [..]
2. Runcirrus executes bsub -- runcirrus --job-dispatch [..]
3. Runcirrus sees --job-dispatch, and does what the job script does today (ie, execute mpirun).