HOTFIX: fix bug in VP test where it greps for the wrong log message

[ableegoldman]

We added more version info to the log messages but must not have cleanly backported the test update -- looking back it seems like older versions might also need a fix (separate PR as the version numbers are different in 2.1-2.3)

PR for 2.1-2.3: #7643

[ableegoldman]

Here's a system test run (one should be sufficient as the error would have caused 100% failure rate): https://jenkins.confluent.io/job/system-test-kafka-branch-builder/3386

[guozhangwang]

@ableegoldman the system test still fails: http://confluent-kafka-branch-builder-system-test-results.s3-us-west-2.amazonaws.com/2019-11-04--001.1572908020--ableegoldman--HOTFIX-fix-message-in-VP-system-test--a986c5c/report.html

[ableegoldman]

Caught another test fix (not actual bug) that was fixed in trunk but slipped from 2.4 -- StreamsUpgradeTest messes around with constructing its own new Subscription objects and needs to encode the ownedPartitions that are normally encoded by the ConsumerCoordinator (KAFKA-9134 strikes again)

[ableegoldman]

New system test: https://jenkins.confluent.io/job/system-test-kafka-branch-builder/3387