Use the file format as the default extension in case the passed in name for the file does not have one.

[rtibbles]

Summary

Description of the change(s) you made

• Fixes small edge case that was showing up for graphie file uploads in ricecooker
• The graphie files' original filename had no extension, so the files were being uploaded to the checksum with no file extension, and then seemed to have not been uploaded.
• This uses the supplied file_format as the default extension to prevent this.

[bjester]

Checked the generate_object_storage_name source, and this looks good to me.