Allow user-supplied configuration data

[blackophelia]

Added support to provide a hash containing user-supplied key/value pairs for use with configuration templates.

Support added for mongodb::server and mongodb::mongos classes.

[atward]

This should be moved below the replset example

[atward]

Shouldn't the mongodb templates be extended to include the values of config_data? eg (for 2.6):

<% @config_data.each do |k,v| -%>
<%= k %>: <%= v %>
<% end -%>

[ekohl]

This now has merge conflicts and needs a rebase.

[atward]

@ekohl rebased against origin/master

[bastelfreak]

Hi @atward, thanks for the rebase. @ekohl should we wait with merging this until #397 is done?