Fix unreliable sleep with proper MockBroker close
Fix unreliable sleep with proper MockBroker close

- close MockBroker in the for loop before validating metrics
- do not add expectation for ProduceRequest (NoResponse)

raisemarketplace/sarama,Shopify/sarama,VividCortex/sarama,VividCortex/sarama,Shopify/sarama,remerge/sarama,remerge/sarama,vrischmann/sarama,DataDog/sarama,HelixEducation/sarama,raisemarketplace/sarama,mailgun/sarama,HelixEducation/sarama,DataDog/sarama,mailgun/sarama,vrischmann/sarama