Use AutoService for creation of Service Loader Metadata

This PR refactors OpenStack/Rackspace APIs/Providers to use AutoService for service loader metadata generation.

- Updated poms with AutoService dependency
- Cleaned up osgi imports in several poms
- Added `@AutoService(ApiMetadata.class)` annotations to APIs
- Added `@AutoService(ProviderMetadata.class)` annotations to Providers

See [jclouds-labs-openstack PR 172](https://github.com/jclouds/jclouds-labs-openstack/pull/172)