Add integration testing for pylint.

Renamed the violation report files to be per-checker. Also added a
pylintrc (which is empty); without it pylint will print a message to
stderr which causes a QualityReporterException. It seems less than
ideal to choke on *any* output to stderr (although we should usually
expect a pylintrc) -- perhaps quality reporters could define a
function to allow certain output, while throwing the exception on
actual errors messages? Seems a minor issue in any case, and maybe
the extra complexity of the BaseQualityReporter interface wouldn't be
worth it.