Add tools.jar to integrationTest classpath for geode-core (#5871)

diff --git a/geode-core/build.gradle b/geode-core/build.gradle
index baf41b8..a908853 100755
--- a/geode-core/build.gradle
+++ b/geode-core/build.gradle
@@ -346,6 +346,8 @@
     testRuntime('commons-validator:commons-validator')
     testRuntime('com.pholser:junit-quickcheck-generators')
 
+    // Needed for JDK8, not JDK11, after nebula.facet v7.0.9
+    integrationTestImplementation(files("${System.getProperty('java.home')}/../lib/tools.jar"))
     integrationTestImplementation(project(':geode-gfsh'))
     integrationTestImplementation(project(':geode-junit'))
     integrationTestImplementation(project(':geode-dunit'))