clear temp files after upload

[shirey]

When files are uploaded for various reasons using file_upload_helper in ingest-api they are added to a temp directory (on PROD /hive/hubmap/hm_uploads_tmp). These temp files aren't being cleared out.

• Ensure that the files are being "committed" to permanent storage (on PROD should be in /hive/hubmap/hm_uploads by current processes/endpoints (if not, fix this before continuing)
• Clear existing temp directory
• Update code such that the temp storage is deleted after an upload is either committed to the permanent storage or reverted (abandoned)