MB-10199 Add sasl bucket authentication support

Added support for retrieving admin sasl auth information via
cb_auth_info:get() api provided by the ns_server and authenticate
password protected buckets using that information.

Change-Id: I032f5174041adad1d21c72108f6ead01f0c7aadb
Reviewed-on: http://review.couchbase.org/35180
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Tested-by: Sarath Lakshman <sarath@couchbase.com>