Refactor: fix namespace of cbsasl

Move everything in cbsasl into the cbsasl namespace to allow
mixing cbsasl and cyrus sasl.

Change-Id: Id3dbe62b923a91f50c4b91dc62716070add59089
Reviewed-on: http://review.couchbase.org/42510
Reviewed-by: Daniel Owen <owend@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>