Add log_handler to implement the publish_errors config option

Synced from Olso.
Commit Id is Ibf28ba17f81b5ddeda653f6a3501ecac18ffcd42

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: Ic97b9c8b84d51c84a53ace5b86cc2e72c744f136
Closes-bug: #1240349
(cherry picked from commit 1c4e279e187d1b864680c9be7849130cb7f12801)
Merge "Add log_handler to implement the publish_errors config option" into stable/havana