Don't wrap SASL creation in assert

Change-Id: I4eb029bfeee21ea5d565d9efc35aab66cb4d0bd3
Reviewed-on: http://review.couchbase.org/28194
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>