[kafka_consumer] refactor private attributes.
[kafka_consumer] refactor private attributes.

DataDog/integrations-core,varlib1/servermall,s-maj/integrations-core,varlib1/servermall,DataDog/integrations-core,DataDog/integrations-core,varlib1/servermall,varlib1/servermall,DataDog/integrations-core,varlib1/servermall,DataDog/integrations-core,serverdensity/sd-agent-core-plugins,serverdensity/sd-agent-core-plugins,s-maj/integrations-core,serverdensity/sd-agent-core-plugins,s-maj/integrations-core,serverdensity/sd-agent-core-plugins,DataDog/integrations-core,DataDog/integrations-core,s-maj/integrations-core,DataDog/integrations-core,s-maj/integrations-core,DataDog/integrations-core,DataDog/integrations-core,serverdensity/sd-agent-core-plugins