IMPALA-286: Display set query options in default section in impala-shell

Options displayed with 'set' command. Default values distinguished
from set values by square brackets.

Change-Id: Iacf0574555aab78aa0ba2008ceb8776d372a57a5
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2889
Reviewed-by: Abdullah Yousufi <abdullah.yousufi@cloudera.com>
Tested-by: jenkins