[SPARK-4990][Deploy]to find default properties file, search SPARK_CONF_DIR first

https://issues.apache.org/jira/browse/SPARK-4990
Used for 

>if [[ "$SPARK_SUBMIT_DEPLOY_MODE" == "client" && -f "$SPARK_SUBMIT_PROPERTIES_FILE" ]]; then
  # Parse the properties file only if the special configs exist
  contains_special_configs=$(
    grep -e "spark.driver.extra*\|spark.driver.memory" "$SPARK_SUBMIT_PROPERTIES_FILE" | \
    grep -v "^[[:space:]]*#"
  )
  if [ -n "$contains_special_configs" ]; then
    export SPARK_SUBMIT_BOOTSTRAP_DRIVER=1
  fi
fi