[GH-174] Used the placeholder in the command help for the name

This issue is created automatically through a Github pull request on behalf of stof:

Url: https://github.com/doctrine/dbal/pull/174

Message:

This change will allow to keep the original help message in DoctrineBundle even if we rename the command. I will submit the same PR for the ORM.

@beberlei please include it in the 2.3 branch (and ideally in 2.2 if it is not too much to ask for it). My goal is to stop duplicating the help messages in the bundle as outdated help messages are really a pain for users (see doctrine/DoctrineBundle#89)