[fb] Log filesystem initialization exceptions

Upon initializing filesystems in Hue's middleware, any exceptions are currently swallowed as a warning: https://github.com/cloudera/hue/blob/master/desktop/core/src/desktop/lib/fsmanager.py#L65-L66

We can't render these as popup exceptions b/c they are caught by the middleware on every request (https://github.com/cloudera/hue/blob/master/desktop/core/src/desktop/middleware.py#L124) in the logic that sets request.fs thus it would actually block the /logs page and every page if an error exists.

Instead, log an actual ERROR and include the original exception details.