CBQE-2446 verify url is live before download binary

Change-Id: I26749b85e3e6577cf7e85faff4ee56e315526929
Reviewed-on: http://review.couchbase.org/42630
Reviewed-by: Thuan Nguyen <soccon@gmail.com>
Tested-by: Thuan Nguyen <soccon@gmail.com>