TestNestmateAttr fails intermittently with jdk_stable group run.

Observed this from JDK11 build 22 onwards, observed same issue in JDK12 also.

Command used to run test case: jtreg/bin/jtreg -dir:jdk11/test/jdk -verbose:summary -nativepath:/utils/testlib/jdk/jtreg/native -exclude:jdk11/test/jdk/ProblemList.txt -r:JTreport -w:JTwork -conc:auto -a -ignore:quiet -timeoutFactor:5 -agentvm -testjdk:jdk-11 :jdk_stable

Logs:
----------System.out:(16/804)----------
vmOpts: '-Xmx512m'
javaOpts: ''
JVM version:11-ea
JDI version: 11.0
JVM description: Java Debug Interface (Reference Implementation) version 11.0
Java Debug Wire Protocol (Reference Implementation) version 11.0
JVM Debug Interface version 11.0
JVM version 11-ea (OpenJDK 64-Bit Server VM, mixed mode)
Target: Testing original Host class from Host
Exception in thread "main" java.lang.NoClassDefFoundError: jdk/test/lib/Asserts
at Target.main(TestNestmateAttr.java:164)
Caused by: java.lang.ClassNotFoundException: jdk.test.lib.Asserts
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:582)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
... 1 more
----------System.err:(22/1375)----------
[22ms] run args: [Target, Host]
[684ms] Note: Unexpected Debuggee Exception: java.lang.ClassNotFoundException at line 582
[717ms] detailMessage = "jdk.test.lib.Asserts"
java.lang.RuntimeException: VM Disconnected before requested event occurred
at TestScaffold.waitForRequestedEvent(TestScaffold.java:742)
at TestScaffold.resumeTo(TestScaffold.java:791)
at TestScaffold.resumeTo(TestScaffold.java:844)
at TestScaffold.startTo(TestScaffold.java:377)
at TestNestmateAttr.runTests(TestNestmateAttr.java:231)
at TestScaffold.startTests(TestScaffold.java:431)
at TestNestmateAttr.main(TestNestmateAttr.java:226)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:115)
at java.base/java.lang.Thread.run(Thread.java:834)

JavaTest Message: Test threw exception: java.lang.RuntimeException: VM Disconnected before requested event occurred
JavaTest Message: shutting down test

STATUS:Failed.`main' threw exception: java.lang.RuntimeException: VM Disconnected before requested event occurred