def set_db2_service(database = nil, username = nil, password = nil)
      self.database  = database
      self.user_name = username
      self.password  = password
      self.service   = Credential::Service::DB2
    end
def set_db2_service(database = nil, username = nil, password = nil)
      self.database  = database
      self.user_name = username
      self.password  = password
      self.service   = Credential::Service::DB2
    end
sets the DB2 service