generate_attributes & remove_procs_from_hash involve a caching of some capistrano variables values

[pavel-rosputko]

Methods from https://github.com/iain/roundsman/blob/master/lib/roundsman/capistrano.rb attempt to leave capistrano variables (
https://github.com/capistrano/capistrano/blob/master/lib/capistrano/configuration/variables.rb) unaffected but does not actually do this.

For example, after an execution of generate_attributes :releases variable defined at
https://github.com/capistrano/capistrano/blob/master/lib/capistrano/recipes/deploy.rb#L60 is evaluated and cached.

This happens because :releases variable is referenced from :current_releases and :previous_release.

This problem is important when combining chef:default and deploy:cold tasks in another task. deploy:cold updates releases but :releases variable value is already evaluated and cached.