Improve MockLogger - level/limited missing method (3)

[andynu]

Improve MockLogger - level/limited missing method

Rails commit bd19d1baf1 [1] added a check of logger.level which was not supported by the MockLogger.

This commit adds a mock level method. And limits the missing_method to respond only to logging calls, so any other calls will raise a NoMethodError to make future debugging easier.

[1] https://github.com/rails/rails/commit/bd19d1baf1cb006f3e9f16afac1c7b4e693f111c

Stacked on #2368