Allow concurrent JSON Import

This is reproducible on Data Center: NA

Steps to Reproduce

• Use two different browsers to simultaneously upload different JSON files using System > External System Import > JSON option

Expected Results

• Both imports should be completed consecutively

Actual Results

• On the browser where the import is performed second, we receive the below error

Configuration information for the importer has been lost (probably due to session timeout). Please restart the import wizard 

Workaround

• Currently, there is no known workaround for this behavior except for waiting for the first import to complete and then starting another one