add Kokoro config for OpenJDK11 (#9837)

* add config for OpenJDK11

kokoro/linux/java_jdk11/build.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+#
+# This is the top-level script we give to Kokoro as the entry point for
+# running the "pull request" project:
+#
+# This script selects a specific Dockerfile (for building a Docker image) and
+# a script to run inside that image.  Then we delegate to the general
+# build_and_run_docker.sh script.
+
+# Change to repo root
+cd $(dirname $0)/../../..
+
+export DOCKERHUB_ORGANIZATION=protobuftesting
+# The image of the Dockerfile sha1 is fetched from the organization
+export DOCKERFILE_DIR=kokoro/linux/dockerfile/test/java_stretch
+export DOCKER_RUN_SCRIPT=kokoro/linux/pull_request_in_docker.sh
+export OUTPUT_DIR=testoutput
+export TEST_SET="java_jdk11"
+./kokoro/linux/build_and_run_docker.sh

kokoro/linux/java_jdk11/continuous.cfg

@@ -0,0 +1,11 @@
+# Config file for running tests in Kokoro
+
+# Location of the build script in repository
+build_file: "protobuf/kokoro/linux/java_jdk11/build.sh"
+timeout_mins: 120
+
+action {
+  define_artifacts {
+    regex: "**/sponge_log.xml"
+  }
+}

kokoro/linux/java_jdk11/presubmit.cfg

@@ -0,0 +1,12 @@
+# Config file for running Linkage Monitor in Kokoro
+# https://github.com/GoogleCloudPlatform/cloud-opensource-java/tree/master/linkage-monitor
+
+# Location of the build script in repository
+build_file: "protobuf/kokoro/linux/java_jdk11/build.sh"
+timeout_mins: 120
+
+action {
+  define_artifacts {
+    regex: "**/sponge_log.xml"
+  }
+}