Add MIG Device support

[zamog]

Adding support for MIG devices - the pull request is still WIP - only to review general idea
#20

[k82cn]

@zamog , that's great! would you help to share more background for this enhancement?

[zamog]

Background:
Multi-Instance GPUs (MIG) allows partitioning GPUs into multiple instances. We saw a significant performance increase when MIG was enabled compared to running a few jobs on the same physical GPU.
More info on Nvidia site

Notes:

1. NVIDIA_VISIBLE_DEVICES changed to use UUID.
2. The memory units must be changed to HundredMB or Gig to support the new GPUs (40/80 Gig)