Bug 1024993 -  Run the CSS Linter in Travis/TBPL

Refactor the script to only report unknown problems
I guess you can just:

files = utils.ls(webapp.sourceDirectoryFile, true, /^(docs|tests?)$/)
                .filter(isCSSFile);

Or Instead of having a isCSSFile method, have a getCSSFilesFor(...) method that hides the listFiles/ls call and the regexp.