Doc resource refactor

This is required to "rebase" #194.

Please make sure to get #306 in first, so we can see if this passes tests.
Should the previous block be combined with this, or do you think they should stay separate because they are accomplishing different things?

I would say re-write the dbpath one above as a one-liner `node.default['mongodb']['config']['dbpath'] = nil if node['mongodb']['is_mongos']`, but it sounds like other attributes should be cleared out as well?