add -J to datalad containers-run

[just-meng]

Would save a lot of run time to have the -J flag enabled, espc. for getting content which is executed implicitly by a call of datalad containers-run.

❮ bash code/reproduce.sh                                                 (base) 
==> Step 1a: Regrid tmax onto RAIN4PE
[ERROR  ] unknown argument: -J 
usage: datalad containers-run [-h] [-n NAME] [-d DATASET] [-i PATH] [-o PATH]
                              [-m MESSAGE] [--expand {inputs|outputs|both}]
                              [--explicit] [--sidecar {yes|no}] [--version]
                              ...

Also mentioned in #163.

EDIT: should link code/reproduce.sh too