Change validators to use the validator_context

Change InstanceKeys to take a namedtuple for context

util/config/validators/validate_database.py

@@ -7,8 +7,10 @@ class DatabaseValidator(BaseValidator):
   name = "database"
 
   @classmethod
-  def validate(cls, config, user, user_password, app):
+  def validate(cls, validator_context):
     """ Validates connecting to the database. """
+    config = validator_context.config
+
     try:
       validate_database_url(config['DB_URI'], config.get('DB_CONNECTION_ARGS', {}))
     except OperationalError as ex: