[QE] io.strimzi.systemtest.upgrade.StrimziUpgradeST.testUpgradeStrimziVersion is sometimes flaky

The test {io.strimzi.systemtest.upgrade.StrimziUpgradeST.testUpgradeStrimziVersion} seems to be sometimes flaky and passes only after severa attempts:

[WARNING] Flakes: 
[WARNING] io.strimzi.systemtest.upgrade.StrimziUpgradeST.testUpgradeStrimziVersion(JsonObject)[9]
[ERROR]   Run 1: StrimziUpgradeST.testUpgradeStrimziVersion:97->performUpgrade:351 KafkaTopic list doesn't have expected size
Expected: is <44>
     but: was <43>
[INFO]   Run 2: PASS

As an example you can see this Jenkins run: https://master-jenkins-csb-amq-streams.cloud.paas.psi.redhat.com/job/strimzi/job/strimzi-pull-request-job/1324

Running it multiple times costs lot of test runtime. But we cannot disable it sicne it is basically half of our upgrade coverage.