Source code refactoring. Extracted common functionality in cpp_helpers.c...

...c and python/python_generator.cc
Move "printer_->Print("))\n\n"); printer_->Outdent();" to PrintServiceClass() and PrintServiceStub().

A print function should print the same number of "("s and closing ")"s (if otherwise its calling function will have no idea whether it should produce extra "("s or ")"s). As this PrintDescriptorKeyAndModuleName() prints no "(", all of ")"s should be moved outside of this function.