Create checkpoints for download_data
Create checkpoints for download_data

Issue #721

david4096/ga4gh-server,saupchurch/server,ohsu-computational-biology/server,dcolligan/server,david4096/ga4gh-server,diekhans/ga4gh-server,dcolligan/server,macieksmuga/server,ohsu-computational-biology/server,david4096/ga4gh-server,macieksmuga/server,dcolligan/server,ga4gh/server,diekhans/ga4gh-server,saupchurch/server,diekhans/ga4gh-server,ga4gh/server,ga4gh/server,saupchurch/server,macieksmuga/server,ohsu-computational-biology/server