Try to use a separate dependency dir

Change-Id: I3b1f48d24fcf9402a4757776aca11275595106bf
Reviewed-on: http://review.couchbase.org/29264
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>