Update Repository 1.1 to return a Promise from new findProviders method.

This commit passes the current, and proposed final Repository 1.1 CT. Note that the org.osgi.util.function.* and org.osgi.util.promise.* classes will be released as part of OSGi Enterprise 6 as a separate jar. As the Repository 1.1 API returns a promise this commit includes the OSGi Promises classes. Once they are released by OSGi they can be removed from the jbosgi-repository codebase.