[FrameworkBundle] do not re-register commands each time a Console\Application is run

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | 
| License       | MIT
| Doc PR        | 

I have been experimenting with using the Symfony console application inside of a React event loop which works quite well.

In this scenario, I re-use an instances of a Console\Application to run multiple tasks. This works well apart from unnecessarily reloading the command classes from all included bundles each time doRun() is called (https://github.com/symfony/symfony/blob/master/src/Symfony/Bundle/FrameworkBundle/Console/Application.php#L68). This can also lead to running out of file descriptors under heavy load as bootstrap.php.cache uses a RecursiveDirectoryIterator to load the command.