Add Kubernetes configuration provider which writes config to a secret

Fixes #145

util/config/provider/baseprovider.py

@@ -24,10 +24,13 @@ def import_yaml(config_obj, config_file):
   return config_obj
 
 
+def get_yaml(config_obj):
+  return yaml.safe_dump(config_obj, encoding='utf-8', allow_unicode=True)
+
 def export_yaml(config_obj, config_file):
   try:
     with open(config_file, 'w') as f:
-      f.write(yaml.safe_dump(config_obj, encoding='utf-8', allow_unicode=True))
+      f.write(get_yaml(config_obj))
   except IOError as ioe:
     raise CannotWriteConfigException(str(ioe))
 
@@ -36,20 +39,24 @@ class BaseProvider(object):
   """ A configuration provider helps to load, save, and handle config override in the application.
   """
 
+  @property
+  def provider_id(self):
+    raise NotImplementedError
+
   def update_app_config(self, app_config):
     """ Updates the given application config object with the loaded override config. """
     raise NotImplementedError
 
-  def get_yaml(self):
-    """ Returns the contents of the YAML config override file, or None if none. """
+  def get_config(self):
+    """ Returns the contents of the config override file, or None if none. """
     raise NotImplementedError
 
-  def save_yaml(self, config_object):
-    """ Updates the contents of the YAML config override file to those given. """
+  def save_config(self, config_object):
+    """ Updates the contents of the config override file to those given. """
     raise NotImplementedError
 
-  def yaml_exists(self):
-    """ Returns true if a YAML config override file exists in the config volume. """
+  def config_exists(self):
+    """ Returns true if a config override file exists in the config volume. """
     raise NotImplementedError
 
   def volume_exists(self):