Print errors when swagger fails to constantize a controller if SHOW_SWAG...

By default errors when constantizing a controller are suppressed. When you run the rake task to generate docs and it does not work because of an error in my controller it would be useful to see the error.

Usually there are many errors I would not be interested in so they should not show by default.

The solution implemented here will only print the errors if a flag SHOW_SWAGGER_ERRORS is set.