[Filesystem] Added a LockHandler

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #9357 , #3586
| License       | MIT
| Doc PR        | https://github.com/symfony/symfony-docs/pull/3956/files

Code sample:

```php
    /**
     * {@inheritdoc}
     */
    protected function execute(InputInterface $input, OutputInterface $output)
    {
        $lockHelper = new LockHandler('/tmp/acme/hello.lock');
        if (!$lockHelper->lock()) {
            $output->writeln('The command is already running in another process.');

            return 0;
        }

        $output->writeln(sprintf('Hello <comment>%s</comment>!', $input->getArgument('who')));

        for (;;) {
        }

        $output->writeln(sprintf('bye <comment>%s</comment>!', $input->getArgument('who')));

        $lockHelper->unlock();
    }
```

![process-lock](https://f.cloud.github.com/assets/408368/2443205/4f0bf3e8-ae30-11e3-9bd4-78e09e2973ad.png)

I think, the $file path should not be composed with the variable `$name` to avoid injection.
If someone use this feature with a `name` generated from request's data without sanitizing it.
example of vunerable code
```
$lockHandler->lock('resource_' . $request->query->get('resource_id');
```
Actualy the class do nothing with the locked file, but an attacker can discover wich file/folder exists or not, and lock system's files. Or if this class is modified in the future (to write pid in the file for instance) it could be dangerous.