tent/cache config read

ok -- to summarize
1. low level caching (with fingerprinting at ...WithIncludes) is pretty much solely for the sake for tests where those files get changed during testing
2. high level (ConfigReader) is the actual caching delivering ultimate speed up since avoid checking/reading configuration files twice.

If just for tests -- why don't we just enable class-wide variable ConfigReader._caching_enabled which would be set/reset by setUp/tearDown methods of corresponding test classes?