LOG4J2-3182 Protect KafkaManager against start failures upon config changes

[wuqian0808]

LOG4J2-3182 Protect KafkaManager against start failures upon config changes.

[wuqian0808]

@garydgregory Raise new clean PR instead. Add all modifications

[vy]

This PR supersedes #593.

[wuqian0808]

a little confused by the title of this PR. It mentions protecting Kafk

Actually if the log4j2 configuration starts failed and with monitorinterval set. The scheduled thread will always increase. I just changed this tittle as requested. But this thread leak logic will affect all.

[garydgregory]

@vy makes a very important point here that I would like to emphasize: if your test passes without the changes to the main tree, then your test does not prove that you've fixed anything.