[release-0.22] Only return true in probe verifier if all partitions found

[knative-prow-robot]

This is an automated cherry-pick of #551

- 🐛 Fix a bug in the consolidated KafkaChannel where some Subscriptions can stay stuck in a `SubscriptionNotMarkedReadyByChannel` state for a long while.

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[knative-metrics-robot]

The following is the coverage report on the affected files.
Say /test pull-knative-sandbox-eventing-kafka-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/channel/consolidated/reconciler/controller/kafkachannel.go	55.2%	55.3%	0.1

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (release-0.22@133ad85). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff               @@
##             release-0.22     #554   +/-   ##
===============================================
  Coverage                ?   73.79%           
===============================================
  Files                   ?      147           
  Lines                   ?     5759           
  Branches                ?        0           
===============================================
  Hits                    ?     4250           
  Misses                  ?     1267           
  Partials                ?      242           

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[matzew]

/lgtm
/approve

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: matzew

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[devguyio]

@googlebot I consent

[devguyio]

/retest