initial pass: users endpoint in oc_erchef

* includes users endpoint support in erchef
* support in underyling components for oc_chef_wm requests
  that do not have a valid org, without stubbing out org.
* make oc_erchef aware of global containers in couch
* nginx routing for endpoints

/ping @opscode/server-team

Note that I'm leaning towards maintaining this as a feature branch
pending completion of other works in progress.