print logging message in lcb_confmon_prepare()

In some situations this function may be called multiple times in
succession (such as when enabling/disabling various providers). Print a
message separating the list of enabled and/or disabled providers.

Change-Id: I81a496521a97d408efb1af44e48aab61d8860324
Reviewed-on: http://review.couchbase.org/38765
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>