stored userdata

I'm envisioning a stored userdata feature.

Currently, OpenStack allow user to execute script or send configuration file
when creating a instance by using --user-data /path/to/filename option.

But,In order to use this option, All users must input userdata every time.
So we need to store the userdata in database so that users can manage userdata more easily.

I'm planning to develop these Nova-APIs.
 - nova userdata-create
 - nova userdata-update
 - nova userdata-delete
 - nova userdata-show
 - nova userdata-list

Users can specify a userdata_name managed by Nova DB or /path/to/filename in --user-data option.

 - nova boot --user-data <userdata_name or /path/to/filename> ...