3818 Delete temporary thumbnail files

[haarli]

What this PR does / why we need it:
With S3 storage activated, Dataverse creates temporary thumbnail files (tempFileForRescale*.tmp) for image and PDF ingests. After the thumbnails are uploaded to S3, the temporary files are not deleted. Our tmp directory currently grew up to over 180GB .

This PR deletes the tempFileForRescale*.tmp files silently after they are uploaded to S3.

Which issue(s) this PR closes:

• partial fix for File Upload: Clean up files left in /tmp after successful ingest #3818

[coveralls]

coverage: 20.331% (-0.001%) from 20.332% when pulling ffad284 on MPDL:IQSS/3818_delete_thumbnail_tmp_files into fd190a3 on IQSS:develop.

[pdurbin]

I didn't test this but the code makes sense.

I'm hitting "approve" but this still need to be prioritized.

@haarli I added it near the top of the community column of the backlog. I hope it helps! Thanks for the pull request!

[sekmiller]

@haarli, we'd like to merge this PR. Can you please update this branch with the latest from develop and see if the Jenkins build succeeds? Thanks!

[haarli]

@sekmiller Sure, the branch is now updated

[pdurbin]

Tests are passing. Will merge. Because @haarli said it's only a partial fix for #3818 I adjusted the description so the issue isn't closed on merge.