fixed GemfireGroupStoreTests.testMultipleInstancesOfGroupStore() test to avoid intermittent failures refactored MessageGroupMetadata to eliminate the usage of TreeMap in favor of LinkedList for storing UUIDs of Messages
fixed GemfireGroupStoreTests.testMultipleInstancesOfGroupStore() test to avoid intermittent failures refactored MessageGroupMetadata to eliminate the usage of TreeMap in favor of LinkedList for storing UUIDs of Messages