This PATCH request seems to include a body. The default JRE implementation will reject such requests. That's why the [OkHttp driver](https://github.com/jclouds/jclouds/pull/251) was added. Have you tried to run a a live test for this method or run it on a real endpoint?

You may have to configure the OkHttp driver to be the default driver for Glance to make this work. There is also [a pull request to add it to Marconi](https://github.com/jclouds/jclouds-labs-openstack/pull/75) you can use as an example.