better more consistent defaults for rackspace and slicehost server models

lib/fog/rackspace/models/servers/server.rb

@@ -65,7 +65,7 @@ module Fog
         end
 
         def save
-          requires :flavor_id, :image_id
+          requires :flavor_id, :image_id, :name
           options = {
             'metadata'    => @metadata,
             'name'        => @name,

lib/fog/slicehost/models/server.rb

@@ -18,6 +18,11 @@ module Fog
       attribute :progress
       attribute :status
 
+      def initialize(attributes={})
+        @flavor_id ||= 1
+        super
+      end
+
       def destroy
         requires :id
         connection.delete_slice(@id)