symfony_deploy_roles in place of symfony_roles

Hello,

I don't know if i do somethings wrong but:

When i have in my deploy.rb :
```
# Role filtering
set :symfony_roles, :web
````
It's don't execute symfony task as controllers_to_clear

But when I put :
```
set :symfony_deploy_roles, :web
```
Its work.

In symfony.rake it 's always fetch this var:

```
on release_roles(fetch(:symfony_deploy_roles)) do
within symfony_web_path do
execute :rm, "-f", *fetch(:controllers_to_clear)
end
end
```

Whereas it's store in other var:

```
role = args[:role] || fetch(:symfony_roles)
```

I am not an expert in ruby that's why i not PR it and i am not sure about it

Start in symfony.rake and compare the role selected from deploy.rb with the role passed to release_roles for controllers_to_clear. Reproduce the behavior using the two configuration snippets, then verify that the documented symfony_roles setting correctly controls the cleanup task.

Written by the indexing model from the issue text.