Hide by default all commands output, except when using -v|-vv|-vvv

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | https://github.com/symfony/symfony-standard/issues/693
| License       | MIT
| Doc PR        | -

Let me explain my reasoning for this change to see if I did it right:

  * @stof remind us that the best solution is to respect the verbosity settings used when running the Composer command ([see comment](https://github.com/symfony/symfony-standard/issues/693#issuecomment-52482253)).
  * In Symfony 2.5 and lower, the commands output their messages, but in 2.6 and higher we want to hide by default all messages.
  * As command output only has to be displayed when using `-v` or `-vv` or `-vvv`, I add the `--quiet` option to the command by default and disable it in case you added any of these tree verbosity flags.

As a side note, I'd like to ask you something: when I touch code in this SensioDistribution bundle I always do it blindly. I don't know how to put the pieces together to check that the new code is working right. Any clue about how to test this?