Add panko and gnocchi as default backend

Default publisher is disabled, because it is hardcoded
in service reclass and uses legacy backends, also database
section is cleaned, with gnocchi ceilometer shouldn't use
any database backends.

Other changes:
  - fixed typo in coordination config
  - added class for configuring polling

Change-Id: I50f73969ed33475703b9c459c7ab4ff9c60eeaeb
Related-Prod: https://mirantis.jira.com/browse/PROD-17731
3 files changed