AWS | storage: make directory.persisted? tell the truth

directory.persisted? was relying on the directory having a key which is almost
always true and not related to storage anyways.

lib/fog/aws/models/storage/directories.rb

@@ -22,7 +22,7 @@ module Fog
             :prefix     => 'prefix'
           })
           data = service.get_bucket(key, options).body
-          directory = new(:key => data['Name'])
+          directory = new(:key => data['Name'], :is_persisted => true)
           options = {}
           for k, v in data
             if ['CommonPrefixes', 'Delimiter', 'IsTruncated', 'Marker', 'MaxKeys', 'Prefix'].include?(k)

lib/fog/aws/models/storage/directory.rb

@@ -108,10 +108,17 @@ module Fog
           end
 
           service.put_bucket(key, options)
+          attributes[:is_persisted] = true
 
           true
         end
 
+        def persisted?
+          # is_persisted is true in case of directories.get or after #save
+          # creation_date is set in case of directories.all
+          attributes[:is_persisted] || !!attributes[:creation_date]
+        end
+
         private
 
         def bucket_location