Testsuite: make IS_J9_JVM variable more robust

So far, this variable is defined by "java.vendor" system property.

IS_J9_JVM = System.getProperty("java.vendor").contains("OpenJ9") || IS_IBM_JVM;

But this detection fails on Eclipse OpenJ9 VM AdoptOpenJDK (where "java.vendor" is "AdoptOpenJDK"). Which leads to the fail of JmxControlledStateNotificationsTestCase testcase in domain module on this JDK.

I suggest to add "java.vm.vendor" property to the previous detection ("Eclipse OpenJ9" on Eclipse OpenJ9 VM AdoptOpenJDK)

Originally, IS_J9_JVM was introduced in WFCORE-4690