Refactor internal configuration struct

It introduces API for pluggable bootstrap workflows

Change-Id: I1742b31089bfe5422b88a015b8891c4d20b57589
Reviewed-on: http://review.couchbase.org/30782
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>