Cannot run batch prediction on selected checkpoint

[vgeorge]

How to replicate:

• Create project
• Run live prediction on a small area
• Retrain a couple times
• Create large new AOI
• Run batch prediction, once completed, its checkpoint will be not the result of the last retrain (passed as parameter to POST /instance), but a new one with parent equal to null

Some captures I did when replicating this bug:

• Batch prediction request, checkpoint_id equal to 158:

• Batch prediction status during processing:

• Batch prediction response payload when completed, the checkpoint_id is 159:

• Newly created checkpoint doesn't have a parent, which make the interface behave as it is the base model:

@LanesGood this issue should be probably the cause of developmentseed/pearl-frontend#126.

cc @ingalls @geohacker