Implement DRMAA v2.2

[natefoo]

Currently only Univa implements 2.2, but it brings a lot of nice improvements, and it'd help adoption if it were implemented for Slurm as well. Specification docs here.

Implementing 2.2 would be a big undertaking and as slurm-drmaa is only a side-project for me (and I'm not a C programmer by trade) I'd say it's fairly unlikely that anything will get done on this, but it's a good goal.