Fixed test issue in GatewayReceiverNamespaceTest class which caused a com.gemstone.gemfire.management.ManagementException: javax.management.InstanceAlreadyExistsException: GemFire:service=GatewayReceiver,type=Member,member=10.237.177.13(80647)-24771 when mocking was disabled and true integration testing was performed in the SDG build/test run.