Add log_handler to implement the publish_errors config option

This handler sends all error logs as rpc notifications.
Note: when using publish_errors you also need to set the
notification_driver option too.

Change-Id: I9ceb1fa92118161779b4b29e2cdc3b91f79ab733
Closes-bug: #1229246
Merge "Add log_handler to implement the publish_errors config option"