500 error when using csv on /data_center/datacenterasset/process_import/

### Steps to reproduce
Importing a csv file will cause a 500 error
Datacenter -> hardware -> import
Choose csv file
it will show you a preview of the stuff that will be imported (its correct here)
confirm import
get 500 error

### Expected behavior

Expected it to bulk import datacenter assets. I was trying to do around 50 at once but I was also getting the same error when only do 3

### Actual behavior

Server Error (500)

### Environment

* Ralph version: Ralph-Core version: 20200129.1
* Operating system: Ubuntu 18.04.3 LTS 4.15.0-74-generic
* Method of installation: Deb package