Expose HTTP REST Idle timeout in lcb_cntl

Change-Id: I59d2d68aa13e3132c6d3121baabaee538a18c02a
Reviewed-on: http://review.couchbase.org/33442
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>