public static VM getBackupVM() {
    return getBackupVM(null);
  }
Return the current primary waiting for a primary to exist and for it not to be the oldPrimary
(if oldPrimary is NOT null).

@since GemFire 5.7
geode-core/src/distributedTest/java/org/apache/geode/internal/cache/tier/sockets/HAInterestTestCase.java