CBD-1199: System for downloading pre-compiled dependencies for build

Change-Id: If5050df78d50b9e56ab4a37143cd4542fcd1ef58
Reviewed-on: http://review.couchbase.org/38792
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Chris Hillery <ceej@couchbase.com>