Allow to set a path for configuration.json

Change-Id: Ie1453b571b7c0c1fa56f45902a4f8ea9c3002605
Reviewed-on: http://review.couchbase.org/33934
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>