Use pre-salted+hashed admin pw for couchdb

bigcouch is a fork of couchdb 1.1 and doesn't have the automatic salting+encryption of plaintext passwords. also, it's nicer to have so puppet doesn't change that resource over and over again.

(from redmine: created on 2013-03-08, closed on 2013-04-24, relates #1942 (closed), blocks #899 (closed))