@Override
            public BlockingQueue<UserGroupInformation> call() throws Exception {
              UserGroupInformation ugi = UserGroupInformation.createRemoteUser(appTokenIdentifier);
              ugi.addToken(appToken);
              BlockingQueue<UserGroupInformation> queue = new LinkedBlockingQueue<>(numExecutors);
              queue.add(ugi);
              LOG.debug("Added new ugi pool for {}. Pool Size: {}", appTokenIdentifier, ugiPool.size());
              return queue;
            }
Get UGI for a given AM and appToken. It is possible to have more than one
UGI per AM.

@param appTokenIdentifier
@param appToken
@return UserGroupInformation
@throws ExecutionException
llap-server/src/java/org/apache/hadoop/hive/llap/daemon/impl/ContainerRunnerImpl.java