Elasticsearch 7.6.1 compatibility

[zhongnansu]

Goal

Prepare release for OD v1.6.0.0/ES 7.6.1

Major Dependency Updates

• ES 7.4.2 -> 7.6.1
• gradle 5.6.2 -> 6.2.1
• JDK 12 -> 13

Issues

There is an undocumented breaking changes since ES 7.5, which will be likely to impact all Open Distro plugins' build process.

Issue 1

Elasticsearch removed the original integTestCluster task. See PRs below for reference.
elastic/elasticsearch#47572
elastic/elasticsearch#47022

To fix this issue, see @dai-chen's branch for a workaround. It commented out the Jacoco integration part for simplicity.

Issue 2

After applying the above solution and uncommented the Jacoco integration code, another issue arises. See my commit

FAILURE: Build failed with an exception.

* Where:
Script '/Users/szhongna/Desktop/Projects/sql/build-tools/sqlplugin-coverage.gradle' line: 99

* What went wrong:
Task with name 'integTest.runner#stop' not found in root project 'opendistro-sql'

Before ES 7.5, there was a gradle task named integTestCluster#stop, and it worked. Since new ES remove integTestCluster as mentioned previously, this no longer works.

If we comment out tasks['integTest.runner#stop'].dependsOn dumpCoverage and try gradle build. It throws the following exception

>Task :integTestRunner
Error: Could not find or load main class  -javaagent:.Users.szhongna.Desktop.Projects.sql.build.tmp.expandedArchives.org.jacoco.agent-0.8.5.jar_6a2df60c47de373ea127d14406367999.jacocoagent.jar=destfile=.Users.szhongna.Desktop.Projects.sql.build.jacoco.integTest.exec,append=true,inclnolocationclasses=false,dumponexit=true,output=file,jmx=true
Caused by: java.lang.ClassNotFoundException:  -javaagent:.Users.szhongna.Desktop.Projects.sql.build.tmp.expandedArchives.org.jacoco.agent-0.8.5.jar_6a2df60c47de373ea127d14406367999.jacocoagent.jar=destfile=.Users.szhongna.Desktop.Projects.sql.build.jacoco.integTest.exec,append=true,inclnolocationclasses=false,dumponexit=true,output=file,jmx=true
Error: Could not find or load main class  -javaagent:.Users.szhongna.Desktop.Projects.sql.build.tmp.expandedArchives.org.jacoco.agent-0.8.5.jar_6a2df60c47de373ea127d14406367999.jacocoagent.jar=destfile=.Users.szhongna.Desktop.Projects.sql.build.jacoco.integTest.exec,append=true,inclnolocationclasses=false,dumponexit=true,output=file,jmx=true
Caused by: java.lang.ClassNotFoundException:  -javaagent:.Users.szhongna.Desktop.Projects.sql.build.tmp.expandedArchives.org.jacoco.agent-0.8.5.jar_6a2df60c47de373ea127d14406367999.jacocoagent.jar=destfile=.Users.szhongna.Desktop.Projects.sql.build.jacoco.integTest.exec,append=true,inclnolocationclasses=false,dumponexit=true,output=file,jmx=true
Process 'Gradle Test Executor 1220' finished with non-zero exit value 1
org.gradle.process.internal.ExecException: Process 'Gradle Test Executor 1220' finished with non-zero exit value 1
        at org.gradle.process.internal.DefaultExecHandle$ExecResultImpl.assertNormalExitValue(DefaultExecHandle.java:417)
        at org.gradle.process.internal.worker.DefaultWorkerProcess.onProcessStop(DefaultWorkerProcess.java:141)
        at org.gradle.process.internal.worker.DefaultWorkerProcess.access$000(DefaultWorkerProcess.java:42)
        at org.gradle.process.internal.worker.DefaultWorkerProcess$1.executionFinished(DefaultWorkerProcess.java:94)
        at jdk.internal.reflect.GeneratedMethodAccessor137.invoke(Unknown Source)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:567)
        at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)
        at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
        at org.gradle.internal.event.AbstractBroadcastDispatch.dispatch(AbstractBroadcastDispatch.java:42)
        at org.gradle.internal.event.BroadcastDispatch$SingletonDispatch.dispatch(BroadcastDispatch.java:231)
        at org.gradle.internal.event.BroadcastDispatch$SingletonDispatch.dispatch(BroadcastDispatch.java:150)
        at org.gradle.internal.event.ListenerBroadcast.dispatch(ListenerBroadcast.java:141)
        at org.gradle.internal.event.ListenerBroadcast.dispatch(ListenerBroadcast.java:37)
        at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)
        at com.sun.proxy.$Proxy49.executionFinished(Unknown Source)
        at org.gradle.process.internal.DefaultExecHandle.setEndStateInfo(DefaultExecHandle.java:221)
        at org.gradle.process.internal.DefaultExecHandle.finished(DefaultExecHandle.java:357)
        at org.gradle.process.internal.ExecHandleRunner.completed(ExecHandleRunner.java:110)
        at org.gradle.process.internal.ExecHandleRunner.run(ExecHandleRunner.java:84)
        at org.gradle.internal.operations.CurrentBuildOperationPreservingRunnable.run(CurrentBuildOperationPreservingRunnable.java:42)
        at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:64)
        at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:48)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
        at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
        at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:56)
        at java.base/java.lang.Thread.run(Thread.java:830)