Please refer to the new test below. This failure looks to be OS independent. Reproduced on both Windows X64 and Linux X64, with different promotion and latest nightly builds.

New test - http://cr.openjdk.java.net/~xiaofeya/8078812/webrev.01/

When running test method testUnnamedApp(), it failed with following error:
test ModuleTest.testAllInModule(): success
Command line: [/java/re/jdk/9/nightly-dev/latest/binaries/linux-x64/bin/java -mp mods -Djava.rmi.server.codebase=file:/net/SCANAS415.us/export/corelibs/users/felix/9-dev/jdk/JTwork/scratch/./mods/mserver/ -cp classes testpkg.DummyApp 37860 ]

Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.NoClassDefFoundError: serverpkg/Hello
at java.lang.Class.getDeclaredMethods0(java.base@9-ea/Native Method)
at java.lang.Class.privateGetDeclaredMethods(java.base@9-ea/Class.java:2937)
at java.lang.Class.privateGetMethodRecursive(java.base@9-ea/Class.java:3282)
at java.lang.Class.getMethod0(java.base@9-ea/Class.java:3252)
at java.lang.Class.getMethod(java.base@9-ea/Class.java:1961)
at sun.launcher.LauncherHelper.validateMainClass(java.base@9-ea/LauncherHelper.java:648)
at sun.launcher.LauncherHelper.checkAndLoadMain(java.base@9-ea/LauncherHelper.java:499)
Caused by: java.lang.ClassNotFoundException: serverpkg.Hello
at jdk.internal.loader.BuiltinClassLoader.loadClass(java.base@9-ea/BuiltinClassLoader.java:366)
at jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(java.base@9-ea/ClassLoaders.java:184)
at java.lang.ClassLoader.loadClass(java.base@9-ea/ClassLoader.java:419)
... 7 more

test ModuleTest.testUnnamedApp(): failure
java.lang.AssertionError: expected [0] but found [1]
at org.testng.Assert.fail(Assert.java:94)
at org.testng.Assert.failNotEquals(Assert.java:494)
at org.testng.Assert.assertEquals(Assert.java:123)
at org.testng.Assert.assertEquals(Assert.java:370)
at org.testng.Assert.assertEquals(Assert.java:380)
at ModuleTest.testUnnamedApp(ModuleTest.java:108)
at sun.reflect.NativeMethodAccessorImpl.invoke0(java.base@9-ea/Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(java.base@9-ea/NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(java.base@9-ea/DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(java.base@9-ea/Method.java:531)
at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:84)
at org.testng.internal.Invoker.invokeMethod(Invoker.java:714)
at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:901)
at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1231)
at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:127)
at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:111)
at org.testng.TestRunner.privateRun(TestRunner.java:767)
at org.testng.TestRunner.run(TestRunner.java:617)
at org.testng.SuiteRunner.runTest(SuiteRunner.java:334)
at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:329)
at org.testng.SuiteRunner.privateRun(SuiteRunner.java:291)
at org.testng.SuiteRunner.run(SuiteRunner.java:240)
at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
at org.testng.TestNG.runSuitesSequentially(TestNG.java:1224)
at org.testng.TestNG.runSuitesLocally(TestNG.java:1149)
at org.testng.TestNG.run(TestNG.java:1057)
at com.sun.javatest.regtest.TestNGAction$TestNGRunner.main(TestNGAction.java:220)
at com.sun.javatest.regtest.TestNGAction$TestNGRunner.main(TestNGAction.java:184)
at sun.reflect.NativeMethodAccessorImpl.invoke0(java.base@9-ea/Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(java.base@9-ea/NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(java.base@9-ea/DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(java.base@9-ea/Method.java:531)
at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:110)
at java.lang.Thread.run(java.base@9-ea/Thread.java:804)
config ModuleTest.shutdownRMIRegistry(): success