Ceilometer dispatcher configurations are there to have gnocchi as
backend but when we use mongodb or mysql dispatcher configurations
are missing.
Closes-Bug: #1640166
(cherry picked from commit d99659050763c71e63ed8b57cbf16d4ce85980fa)
Change-Id: I9cdfc6e2208978e72b76bff7f6a1cba80386ffa8