Add support for OAR Scheduler

[ychiat35]

The Oar scheduler is widely used in France, including mesocentre supercomputers (e.g., GRICAD), INRIA supercomputers, Grid5000 testbed and other platforms.

Nypipe does have a OAR plugin here: https://github.com/nipy/nipype/blob/master/nipype/pipeline/plugins/oar.py

We created this PR , to add support for the OAR Scheduler, following the implementation made for Slurm.