Remove 'always_on' flag

This can be inferred by setting the idle timeout to -1

Change-Id: I07737df2d8972c6d3153f75f3007ee566545d06d
Reviewed-on: http://review.couchbase.org/34955
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>