Add support for client side sasl

Change-Id: I776fde0531b106efbfdd2d0bd3eeb72573b2f34f
Reviewed-on: http://review.couchbase.org/28925
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Michael Wiederhold <mike@couchbase.com>