cntl: sasl info is const char *

Fixes compilation warnings

Change-Id: Idb7bf6a42d596bb821de73543d9f5f52189311a2
Reviewed-on: http://review.couchbase.org/35876
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>