Default Sqlite metadata database doesn't use configured --storage directory

[da4089]

If using the --storage option, and defaulting to Sqlite database, the metadata.db file is always created as packages/metadata.db regardless of what --storage path was specified.

Using the STORAGE environment places the metadata file into the specified directory.

The reason is that the database options definition uses the default_storage path, which will default to packages unless STORAGE is set, but since the options aren't parsed yet, the --storage value is ignored.

As a user, this is a little surprising -- I'd expected STORAGE and --storage to have the same effect.

I think the best solution would be to defer constructing the database URL until after options parsing, in server.py?