FileBrowser add file functionality fails if DataSet's sources haven't been translated to their corresponding s3 upload buckets

[scottx611x]

• Specific code commit: 4d61e10
• Version of the web browser and OS: N/A
• Environment where the error occurred (Vagrant VM and site conf mode or AWS instance): test.stemcellcommons.org

Steps to reproduce

Please list all the actions and the input data used:

• Upload a dataset: (hg19-metadata-local.txt) and import at least one of its corresponding datafiles (s5_p42_E2_45min.subsample.fastq) as part of the import process.
• Notice that all of the DataSet's FileStoreItem's sources will get mapped from /data/import/... to their new s3://release-1-6-5-testing-upload/..... ones once they get a file_source_translator from generate_file_source_translator() during the metadata parsing phase.
• You can then properly use the add files functionality from the FileBrowser UI for all Nodes in the DataSet.

Observed behavior

• If you upload the same DataSet without importing any data files, the FileStoreItem sources will remain "untranslated" (/data/import/...) and you won't be able to add any files from the FileBrowser UI.

• It would be up to AddFileToNodeView and the .js that POSTs to it to do the file source translation and sending over of the Cognito identity_id, respectively.

Expected behavior

• To be able to add data files in the FileBrowser UI when this edge case occurs

[scottx611x]

Closed in #2890