Upload Files page: Error 500 on reload after deleting file

[adswafford]

Steps to reproduce:
Upload file
Navigate to another page
Return to Upload Files page
Select the file and delete it
Refresh page with browser button
Error 500 appears

[antgonza]

Confirmed the error. However, IMOO this is a complete PEBCAK: Basically, the user has to:

1. Ignore to not use the browser buttons
2. Delete something and they reload the page
3. Once the page is gonna be reloaded, confirm twice, that they want to resubmit the last page - cause this is a POST command.

Anyway, the solution is pretty simple:
Do not raise this error here: https://github.com/biocore/qiita/blob/master/qiita_db/util.py#L505 and simply don't rename the file.

[antgonza]

Fixed in #2466