Add doc description for stop_timeout_before_update
Add doc description for stop_timeout_before_update

Update documentation to add stop_timeout_before_update config paramater.

Change-Id: I3f3c7d43c7d732fc712a916a25c762f531118a22

openstack/senlin,openstack/senlin,openstack/senlin,stackforge/senlin,stackforge/senlin