Fix the leadership integration test with Java 11

[jihoonson]

Description

The leadership integration test starts failing with Java 11 such as in here. It is because of the custom node failed with OOM.

java.lang.OutOfMemoryError: Java heap space
Dumping heap to /tmp/java_pid906.hprof ...
Heap dump file created [46020040 bytes in 0.143 secs]
Terminating due to java.lang.OutOfMemoryError: Java heap space

This PR increases the heap from 32m to 64m.

---

This PR has:

• been self-reviewed.
  • using the concurrency checklist (Remove this item if the PR doesn't have any relation to concurrency.)
• added documentation for new or modified features or behaviors.
• added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links.
• added or updated version, license, or notice information in licenses.yaml
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added unit tests or modified existing tests to cover new code paths, ensuring the threshold for code coverage is met.
• added integration tests.
• been tested in a test Druid cluster.

[jihoonson]

As this issue is another blocker for 0.21.0, I couldn't wait for Travis to run, so went ahead and ran the same jobs on the internal CI of Imply. All tests passed except for (Compile=openjdk8, Run=openjdk11) input source integration test, which seems like a temporary connection issue. This test uses https://druid.apache.org/data/wikipedia.json.gz. The detailed error is in below. The same test passed on my local machine.

java.lang.RuntimeException: java.net.ConnectException: Connection timed out (Connection timed out)
	at org.apache.druid.data.input.impl.InputEntityIteratingReader.lambda$read$0(InputEntityIteratingReader.java:81) ~[druid-core-0.22.0-iap1-SNAPSHOT.jar:0.22.0-iap1-SNAPSHOT]
	at org.apache.druid.java.util.common.parsers.CloseableIterator$2.findNextIteratorIfNecessary(CloseableIterator.java:84) ~[druid-core-0.22.0-iap1-SNAPSHOT.jar:0.22.0-iap1-SNAPSHOT]
	at org.apache.druid.java.util.common.parsers.CloseableIterator$2.<init>(CloseableIterator.java:69) ~[druid-core-0.22.0-iap1-SNAPSHOT.jar:0.22.0-iap1-SNAPSHOT]
	at org.apache.druid.java.util.common.parsers.CloseableIterator.flatMap(CloseableIterator.java:67) ~[druid-core-0.22.0-iap1-SNAPSHOT.jar:0.22.0-iap1-SNAPSHOT]
	at org.apache.druid.data.input.impl.InputEntityIteratingReader.createIterator(InputEntityIteratingReader.java:103) ~[druid-core-0.22.0-iap1-SNAPSHOT.jar:0.22.0-iap1-SNAPSHOT]
...

[suneet-s]

+1 on not waiting for travis on this change

[jihoonson]

@jon-wei @clintropolis @suneet-s @maytasm thank you all!