MB-100 add operating_system field in ini file

Change-Id: I5256926c54c22b15fc8bb397a7298851b2573dcc
Reviewed-on: http://review.couchbase.org/27185
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Thuan Nguyen <soccon@gmail.com>