Implements the XMPP Ping as defined by XEP-0199. This protocol offers an
alternative to the traditional 'white space ping' approach of determining the
availability of an entity. The XMPP Ping protocol allows pings to be
performed in a more XML-friendly approach, which can be used over more than
one hop in the communication path.
Returns an Iterator (of String) with the supported features by the server. The features to
include are the features offered and supported protocols by the SERVER. The idea is that
different modules may provide their features that will ultimately be part of the features
offered by the server.