use sys function for exit instead of helper

see http://docs.python.org/2/library/constants.html#constants-added-by-the-site-module
for details

Change-Id: Ieb81434e530e54ba8f8bdbdca10695f96874c1bc
Reviewed-on: http://review.couchbase.org/34102
Reviewed-by: Aaron Miller <apage43@ninjawhale.com>
Tested-by: Aaron Miller <apage43@ninjawhale.com>