Fix batch_size configuration option in Docker
Fix batch_size configuration option in Docker

The configuration option name for Kafka batch size (max. number of
messages before commiting them to Kafka broker) has been changed in
Queens release. The option passed to Docker image must reflect that.

Change-Id: Ib720c4d0358a5e67734fbc38d9a7d513e662d65f
Story: 2007225
Task: 38492

openstack/monasca-persister,openstack/monasca-persister,openstack/monasca-persister