Download 3rd-party deps by default

Change-Id: I9f7d742481916c70cbd80c1e4d2ac81c972dec2a
Reviewed-on: http://review.couchbase.org/43668
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Chris Hillery <ceej@couchbase.com>