Sync log_handler from Oslo

Resolves an ImportError when enabling publish_errors for
Ceilometer services. Essentially, PublishErrorsHandler was
moved in Oslo from *.log to *.log_handler, but log_handler
was not yet being pulled in.

Oslo commit: Ibf28ba17f81b5ddeda653f6a3501ecac18ffcd42

Change-Id: I23bc7fd0ea4c811e133e743634032fb836c34b22
Fixes: Bug #1244722