enforce required config

lib/ansible/config/manager.py

@@ -343,6 +343,15 @@ class ConfigManager(object):
 
             # set default if we got here w/o a value
             if value is None:
+                if defs[config].get('required', False):
+                    entry = ''
+                    if plugin_type:
+                        entry += 'plugin_type: %s ' % plugin_type
+                        if plugin_name:
+                            entry += 'plugin: %s ' % plugin_name
+                    entry += 'setting: %s ' % config
+                    raise AnsibleError("No setting was provided for required configuration %s" % (entry))
+                else:
                     value = defs[config].get('default')
                     origin = 'default'
                     # skip typing as this is a temlated default that will be resolved later in constants, which has needed vars