Fix case expected for XCOM_PUSH (#575)

and add spaces to avoid issues with empty variables

script/entrypoint

@@ -29,7 +29,7 @@ elif [ "$1" = "query" ]; then
     # to
     #     bq query [options] < FILE
     exec bq "${@:1:$#-1}" < "${@: -1}"
-elif ["$XCOM_PUSH" = "True"]; then
+elif [ "$XCOM_PUSH" = "true" ]; then
     # KubernetesPodOperator will extract the contents of /airflow/xcom/return.json as an xcom
     # if the xcom_push parameter is true
     mkdir -p /airflow/xcom/ && touch /airflow/xcom/return.json