Log indexing exceptions at 'exception' level
Log indexing exceptions at 'exception' level

Stack traces are swallowed when there's an error indexing a plugin.
Log exceptions at 'exception' level rather than 'error' to get better
diagnostic information during interactive index syncs.

Change-Id: I53cc44a07a5bb9a9488b91564180664bbeab80af

openstack/searchlight,openstack/searchlight,openstack/searchlight