Rename mc_SASL* stuff to mc_SESS* stuff

Session initialization will do more than SASL now

Change-Id: Ib2dd39336554583375fd11d06728d06b33232485
Reviewed-on: http://review.couchbase.org/37618
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>