private static String getMd5(List<String> lines) {
        return ConfigUtils.getMd5(skipEmptyLines(lines));
    }
Computes Md5 hash of a list of strings. The only change to input lines before
computing md5 is to skip empty lines.

@param lines A list of lines
@return the Md5 hash of the list, with lowercase letters
config/src/test/java/com/yahoo/vespa/config/util/ConfigUtilsTest.java