added support to hector exceptions to display the host

Added a CassandraHost reference to HectorException along with getHost() and setHost() methods, and overrode getMessage() to prefix the message with the host if its not null.  Added a second method to ExceptionsTranslator that takes a host along with a Throwable, and modified ExceptionsTranslatorImpl to push the host into the exceptions that are returned.  Also modified HConnectionManager to use this method by trying to detect the host from the pool or client if possible.