move alias registration into a separate register() method

lib/vagrant/alias.rb

@@ -15,22 +15,28 @@ module Vagrant
           # separate keyword-command pairs
           keyword, command = line.split("=").collect(&:strip)
 
-          @aliases.register(keyword.to_sym) do
-            lambda do |args|
-              # directly execute shell commands
-              if command.start_with?("!")
-                return exec "#{command[1..-1]} #{args.join(" ")}".strip
-              end
-
-              return CLI.new(command.split.concat(args), env).execute
-            end
-          end
+          register(keyword, command)
         end
       end
     end
 
+    # This returns all the registered alias commands.
     def commands
       @aliases
     end
+
+    # This registers an alias.
+    def register(keyword, command)
+      @aliases.register(keyword.to_sym) do
+        lambda do |args|
+          # directly execute shell commands
+          if command.start_with?("!")
+            return exec "#{command[1..-1]} #{args.join(" ")}".strip
+          end
+
+          return CLI.new(command.split.concat(args), env).execute
+        end
+      end
+    end
   end
 end