stats_hero fixes

GET /organizations/:orgname/users was not returning #base_state

This request brings the code to oc_chef_wm_org_associations:to_json()
for which one path returned a #association_state{} instead of a
 #base_state{}. This causes chef_wm:finish_request() to fail to
pattern match, thus never executing finish_request()

This change makes sures it returns a #base_state{} instead.