MINOR: fix verifiable consumer assertion
MINOR: fix verifiable consumer assertion

Author: Jason Gustafson <jason@confluent.io>

Reviewers: Guozhang Wang

Closes #597 from hachikuji/fix-verifiable-consumer-assertion

(cherry picked from commit 78e7f87db8be3b1eae59752e8c9ceb0b8c064a96)
Signed-off-by: Guozhang Wang <fae442ba222671b2ebdf7511c9ca77079c43031b@gmail.com>

racker/kafka,racker/kafka,racker/kafka,racker/kafka