ensure all API errors are reported with a json message
When a user tries to download a file in the datastore that doesn't exist using the API a 404 error is returned.
<html>
<head><title>404 Not Found</title></head>
<body bgcolor="white">
<center><h1>404 Not Found</h1></center>
<hr><center>nginx/1.10.3</center>
</body>
</html>
This error should be returned in a JSON format.
Edited by BAIRE Anthony