Add a command line option to control role filtering

The functionality to filter the executing tasks by role (i.e. deploying
only to servers that match the role you specify) already exists. It can
specified either by using the following in your deployment config:

    set :filter, :roles => %w{app web}

Or by setting `ENV['ROLES']`:

    ROLES=app,web cap production deploy

This commit adds a command line switch to set the role filter, which
avoids polluting ENV:

    cap --roles=app,web production deploy

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 Reverse Chronological Order:
 
+## master
+
+  * Add a command line option to control role filter (`--roles`) (@andytinycat)
+
 ## `3.1.0` (not released)
 
   * Tasks `deploy:linked_dirs`, `deploy:make_linked_dirs`, `deploy:linked_files`, `deploy:cleanup_rollback`,

lib/capistrano/application.rb

@@ -13,7 +13,7 @@ module Capistrano
     end
 
     def sort_options(options)
-      options.push(version,dry_run)
+      options.push(version,dry_run,roles)
       super
     end
 
@@ -63,6 +63,15 @@ module Capistrano
        }
       ]
     end
+    
+    def roles
+      ['--roles ROLES', '-r',
+       "Filter command to only apply to these roles (separate multiple roles with a comma)",
+       lambda { |value|
+         Configuration.env.set(:filter, :roles => value.split(","))
+       }
+      ]
+    end
   end
 
 end