added search of variable

...sMetadataService/api/control_unit/SearchInstancesByUS.cpp

ChaosMetadataService/api/data_service/GetAllDataService.cpp

ChaosMetadataService/api/data_service/GetAssociationByDS.cpp

ChaosMetadataService/api/node/NodeSearch.cpp

ChaosMetadataService/api/service/GetVariable.cpp

ChaosMetadataService/api/service/RemoveVariable.cpp

ChaosMetadataService/api/service/SearchVariable.cpp

ChaosMetadataService/api/service/SearchVariable.h

ChaosMetadataService/api/service/SetVariable.cpp

...tadataService/persistence/data_access/UtilityDataAccess.h

...dataService/persistence/mongodb/MongoDBNodeDataAccess.cpp

...aService/persistence/mongodb/MongoDBUtilityDataAccess.cpp

...ataService/persistence/mongodb/MongoDBUtilityDataAccess.h

ChaosMetadataServiceClientTest/NodeSearchTest.cpp

ccs/data/SearchNodeListModel.cpp

ccs/node/data_service/DataServiceEditor.cpp

ccs/node/unit_server/UnitServerEditor.cpp

chaos/common/chaos_constants.h

chaos/common/message/MDSMessageChannel.cpp