Exit cpplint only after checking all files

[r-shah22]

Currently, cpplint exits immediately after finding an error in a single file. I have changed it so that it completes checking all the files and showing all of the errors rather than exiting on the first problematic file found.

The current design is quite inconvenient because when you have multiple files that could potentially have errors, it will only show you the errors one file at a time. If the errors in all files were showed in one go, they can be corrected in one go, and would avoid the user attempting to commit multiple times until all the files are eventually fixed.