local composer installation not detected

_Issue_ : The generator does not detect a local composer.phar file priorly installed.

 _Replication steps_ : 
- create a `test` directory
- in this directory, execute `curl -sS https://getcomposer.org/installer | php`
- execute `yo joli-symfony` 

_Expected_ : the generator detects the composer.phar in fs root, so does not prompt for composer installation and use the existing phar
