Review changes

* changing log.fatal() to log.warn()

* custom message to log.error(msg, e)

* license header to difference.rb in puppet module

* made obsoleted member expiry time configurable

* log.warn() when cluster monitor creation failed

* changing log.debug() to log.error() when cluster monitor not found, while receiving topology and health stats events   
This is fixed now. Thanks Imesh for pointing this out.