8055275: Several gc/class_unloading/ tests fail due to missed +UnlockDiagnosticVMOptions flag

Reviewed-by: mgerdin, jwilhelm

test/gc/class_unloading/TestCMSClassUnloadingEnabledHWM.java

@@ -45,6 +45,7 @@ public class TestCMSClassUnloadingEnabledHWM {
   private static OutputAnalyzer run(boolean enableUnloading) throws Exception {
     ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
       "-Xbootclasspath/a:.",
+      "-XX:+UnlockDiagnosticVMOptions",
       "-XX:+WhiteBoxAPI",
       "-XX:MetaspaceSize=" + MetaspaceSize,
       "-Xmn" + YoungGenSize,

test/gc/class_unloading/TestG1ClassUnloadingHWM.java

@@ -45,6 +45,7 @@ public class TestG1ClassUnloadingHWM {
   private static OutputAnalyzer run(boolean enableUnloading) throws Exception {
     ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
       "-Xbootclasspath/a:.",
+      "-XX:+UnlockDiagnosticVMOptions",
       "-XX:+WhiteBoxAPI",
       "-XX:MetaspaceSize=" + MetaspaceSize,
       "-Xmn" + YoungGenSize,