Ensure buildbot can sudo without a tty

Change-Id: Ie5e09c52cddca9bfb6299bae25a3f9d6c2aa5700
Reviewed-on: http://review.couchbase.org/40556
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Chris Hillery <ceej@couchbase.com>