Changes to CodeSniffRunner

[bmitch]

This class and the test classes could be cleaned up:

• To get the error count and warning count you have to run the sniff twice. Should only have to do it once.
• Can we get the error and warning message so that can be tested?

The code where it runs a sniff looks messy. Can this be cleaned up?

        $errorCount = $codeSnifferRunner->detectErrorCountInFileForSniff(
            __DIR__.'/Assets/FunctionLengthSniff/FunctionLengthSniff.inc',
            'Codor.Files.FunctionLength'
        );