KAFKA-7660: fix streams and Metrics memory leaks

[vvcephei]

Backport two memory-leak fixes (#5974 and #5953) (see also 2.1: #5979, 2.0: #5980 )

It looks like we already had the parentSensors fix in 1.1 and lost it in 2.0. The change in
this PR just tidies it up a little for consistency with later branches.

Committer Checklist (excluded from commit message)

• Verify design and implementation
• Verify test coverage and CI build status
• Verify documentation (including upgrade notes)

[vvcephei]

@mjsax @guozhangwang , This is an even further backport of a couple of small memory-leak fixes from trunk.

I'm not sure if you want to keep them as separate commits in the backport as well...

[vvcephei]

@ijuma The 1.1 branch builder also looks misconfigured:

JDK10 (same failure as #5980 (comment)):

00:00:59.333 * What went wrong:
00:00:59.333 Task 'findbugsMain' not found in root project 'kafka-pr-jdk10-scala2.12'.

JDK7:

00:00:40.343 /tmp/jenkins8716077406695918171.sh: line 4: /home/jenkins/tools/gradle/4.4/bin/gradle: No such file or directory

Any idea how we can get this fixed?

[ijuma]

@vvcephei I replied to the first issue in another PR (btw, it's not necessary to point out the same problem in lots of different PRs :)). For the second one, it looks like Gradle 4.4 was removed from the build machines. I updated the job to use Gradle 4.10.2 to bootstrap.

[ijuma]

retest this please

[ijuma]

retest this please

[vvcephei]

java 7 failure looks unrelated:

kafka.admin.DeleteConsumerGroupTest.testConsumptionOnRecreatedTopicAfterTopicWideDeleteInZK

kafka.consumer.ConsumerTimeoutException
	at kafka.consumer.ConsumerIterator.makeNext(ConsumerIterator.scala:70)
	at kafka.consumer.ConsumerIterator.makeNext(ConsumerIterator.scala:34)
	at kafka.utils.IteratorTemplate.maybeComputeNext(IteratorTemplate.scala:64)
	at kafka.utils.IteratorTemplate.hasNext(IteratorTemplate.scala:56)
	at kafka.utils.IteratorTemplate.next(IteratorTemplate.scala:36)
	at kafka.consumer.ConsumerIterator.next(ConsumerIterator.scala:47)
	at kafka.admin.DeleteConsumerGroupTest$$anonfun$consumeEvents$1.apply(DeleteConsumerGroupTest.scala:218)
	at kafka.admin.DeleteConsumerGroupTest$$anonfun$consumeEvents$1.apply(DeleteConsumerGroupTest.scala:218)
	at scala.collection.immutable.Range.foreach(Range.scala:160)
	at kafka.admin.DeleteConsumerGroupTest.consumeEvents(DeleteConsumerGroupTest.scala:218)
	at kafka.admin.DeleteConsumerGroupTest.testConsumptionOnRecreatedTopicAfterTopicWideDeleteInZK(DeleteConsumerGroupTest.scala:182)

stdout:
[2018-12-02 20:32:18,952] ERROR ZKShutdownHandler is not registered, so ZooKeeper server won't take any action on ERROR or SHUTDOWN server state changes (org.apache.zookeeper.server.ZooKeeperServer:472)
[2018-12-02 20:32:19,150] WARN Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect (org.apache.zookeeper.ClientCnxn:1162)
java.net.ConnectException: Connection refused
	at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
	at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:744)
	at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:361)
	at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1141)
...

Retest this, please.