CDH-21036: Make --quiet flag suppress warning messages in impala-shell

Change-Id: Ia57652840b3e3483a06c0bbef283c60a229db27f
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/4092
Reviewed-by: Abdullah Yousufi <abdullah.yousufi@cloudera.com>
Tested-by: jenkins