Removed Zookeeper Discovery Provider

The Zookeeper Discovery Provider was based upon the Apache Zookeeper library with a very old version. This old version of Apache Zookeeper had a number of bugs and the old version has/had been removed from the Eclipse Orbit Project. The resources were not available to update the discovery provider to a more recent version, and so it was removed from further distribution. For consumers that require it, please see the release 3.14.41 at https://download.eclipse.org/rt/ecf/3.14.41

Enhanced org.eclipse.ecf.ssl support for default context

See pull request https://github.com/eclipse/ecf/pull/106