Add test tasks for unpooled and direct buffer pooling to netty

Some netty behavior is controlled by system properties. While we want to
test with the defaults for Elasticsearch for most tests, within netty we
want to ensure these netty settings exhibit correct behavior. This
commit adds variants of test and integTest tasks for netty which set the
unpooled and direct buffer pooled allocators.

relates elastic#45881

Author: rjernst

modules/transport-netty4/build.gradle

@@ -17,6 +17,8 @@
  * under the License.
  */
 
+import org.elasticsearch.gradle.test.RestIntegTestTask
+
 /*
  TODOs:
    * fix permissions such that only netty4 can open sockets etc?
@@ -67,6 +69,35 @@ integTestRunner {
     systemProperty 'io.netty.allocator.numDirectArenas', '0'
 }
 
+TaskProvider<Test> unpooledTest = tasks.register("unpooledTest", Test) {
+  include '**/*Tests.class'
+  systemProperty 'es.set.netty.runtime.available.processors', 'false'
+  systemProperty 'io.netty.allocator.type', 'unpooled'
+}
+TaskProvider<Test> directBufferPoolingTest = tasks.register("directBufferPoolingTest", Test) {
+  include '**/*Tests.class'
+  systemProperty 'es.set.netty.runtime.available.processors', 'false'
+  systemProperty 'io.netty.allocator.numDirectArenas', '2'
+}
+// TODO: we can't use task avoidance here because RestIntegTestTask does the testcluster creation
+RestIntegTestTask unpooledIntegTest = tasks.create("unpooledIntegTest", RestIntegTestTask) {
+  runner {
+    systemProperty 'es.set.netty.runtime.available.processors', 'false'
+  }
+}
+testClusters.unpooledIntegTest {
+  systemProperty 'io.netty.allocator.type', 'unpooled'
+}
+RestIntegTestTask directBufferPoolingIntegTest = tasks.create("directBufferPoolingIntegTest", RestIntegTestTask) {
+  runner {
+    systemProperty 'es.set.netty.runtime.available.processors', 'false'
+  }
+}
+testClusters.directBufferPoolingIntegTest {
+  systemProperty 'io.netty.allocator.numDirectArenas', '2'
+}
+check.dependsOn(unpooledTest, directBufferPoolingTest, unpooledIntegTest, directBufferPoolingIntegTest)
+
 thirdPartyAudit {
     ignoreMissingClasses (
         // classes are missing