default_data.schema.json can be used for checking the config file
default_data.json. The check will be able to block an error on
stackalytics-processor internally. The schema should not exist
as a config file, so this patch makes the schema hard-coded.
NOTE: The copyright of schema.py comes from the initial version of
default_data.schema.json: I7b5104b25fecc6a7da7c025bf48f72885c1fbebc
Change-Id: Ia98c6d9ce2cec3bac80ff9159f854b1a65b6a4d8