log about .mongo-setup-complete

When mongo has already been setup once we have the following message when trying to call it twice:

    $ /usr/sbin/oo-mongo-setup
    I, [2013-05-15T13:09:41.928062 #25353]  INFO -- : Mongo has already been setup on this machine. Exiting


It would be useful to inform the user about the presence of the lock file `/etc/openshift/.mongo-setup-complete`.

It would avoid to look at the sources.