1. Add collect_statistics_interval and rates_mode configurations in
rabbitmq.config template which enables to define custom value for
those fields.
2. Add collect_statistics_interval and rates_mode defaults in
defaults/main.yml
Change-Id: Ie349528929398f53a9d87e7fc02e0c95c9d6d4f1
Closes-bug: 1617516
(cherry picked from commit 9ccc0ee3f1)