Honor the :no_release setting on a server

This allows a user to flag a server with `:no_release => true` to bypass
relase tasks. The method used to accomplish this was copied from
[capistrano/bundler](https://github.com/capistrano/bundler/blob/master/lib/capistrano/tasks/bundler.cap#L64-L65)
Merge pull request #4 from devin-c/honor_no_release

Honor the :no_release setting on a server