NCBC-727: Make CTOR that takes CouchbaseClientSection public

Change-Id: Iaaf26a0192b0bbdc5083a9d87cf3b837879163ad
Reviewed-on: http://review.couchbase.org/43654
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>