Add java-gradle-plugin for kotlin-gradle-plugin tasks validation;

Make task properties validation fail on warnings; run it during IT

libraries/tools/kotlin-gradle-plugin-integration-tests/build.gradle

@@ -28,6 +28,9 @@ dependencies {
     testRuntime project(path: ':kotlin-android-extensions', configuration: 'runtimeJar')
 }
 
+// Include Gradle task properties validation into the testing procedure:
+test.dependsOn(":kotlin-gradle-plugin:validateTaskProperties")
+
 test.dependsOn(":kotlin-allopen:install",
                ":kotlin-android-extensions:install",
                ":kotlin-build-common:install",
@@ -40,6 +43,7 @@ test.dependsOn(":kotlin-allopen:install",
                ":kotlin-stdlib-jre8:install",
                ":examples:annotation-processor-example:install")
 
+
 // Validate that all dependencies 'install' tasks are added to 'test' dependencies
 // Test dependencies are specified as paths to avoid forcing dependency resolution
 // and also to avoid specifying evaluationDependsOn for each testCompile dependency.