function removeDirectoryIfExists (dirPath, cb) {
    fs.exists(dirPath, function(exists){
        if (exists) {
            removeForcefully(dirPath, cb);
        } else {
            cb();
        }
    });
}
Executes a child process to forcefully remove
a directory containing files

@param  {String}   dirPath The path of the directory to remove
@param  {Function} cb      The function to execute when finished
@return {Void}