Imported custom theme inherits original uid/gid of tgz

[Nobuto Murata]

By using the custom theme functionality of the charm:
juju attach-resource openstack-dashboard theme=./custom-theme.tgz

The destination ends up with the original uid/gid of the state where the tgz was created (in this case uid/gid = 1000).

root@juju-8a8f85-1-lxd-5:/usr/lib/python3/dist-packages/openstack_dashboard/themes# ll -n
total 28
drwxr-xr-x 7 0 0 4096 Jan 31 11:55 ./
drwxr-xr-x 20 0 0 4096 Jan 30 13:23 ../
drwxrwxr-x 3 1000 1000 4096 Jan 31 08:01 custom/
drwxr-xr-x 3 0 0 4096 Jan 30 13:22 default/
drwxr-xr-x 4 0 0 4096 Jan 30 13:22 example/
drwxr-xr-x 4 0 0 4096 Jan 30 13:22 material/
drwxr-xr-x 5 0 0 4096 Jan 30 13:22 ubuntu/

We might want to reset the uid/gid to 0 (root) when extracting it. However, the theme can contain some python scripts there under the framework of horizon so I'm not 100% sure if it's safe to import it as root always.