[Docker] fix @_NOT_FOUND_@ hack in config.rb
docker/build_tools/config.rb script substitutes the string
@_NOT_FOUND_@ for any configuration variable required that isn't found in
It's an ugly hack that causes some confusing downstream problems: for example, if this string appears as the value of a field in
application.yml, it produces this error when trying to build the API server image:
rake aborted! Psych::SyntaxError: (<unknown>): found character that cannot start any token while scanning for the next token at line 53 column 22 /usr/src/arvados/services/api/config/initializers/zz_load_config.rb:7:in `block in <top (required)>'
A better solution would be to raise an exception, forcing the user to correct the problem immediately at config time. Alternatively, substitute a syntactically valid string like
VARIABLE_NOT_FOUND which can be parsed, but is at least likely to appear in error messages in a way that will make it easier to trace to their source.