title: Joda DateTimeFormatter.parseDateTime is failing for General time zone('z')
body: <p>Confused with the use of General time zone('z'). Joda is failing in below sample code. Can somebody help me to understand why the behavior is like this? How can I parse a date in differnt timezone using this format in Joda?</p>
  
  <pre><code>    public static void main(String[] args) throws ParseException {
          SimpleDateFormat sdf = new SimpleDateFormat("yyyy.MM.dd G 'at' HH:mm:ss z");
          System.out.println(sdf.parse("2019.09.17 AD at 15:29:00 IST"));
  
          DateTimeFormatter pattern = DateTimeFormat.forPattern("yyyy.MM.dd G 'at' HH:mm:ss z");
          DateTime dateCtxParamDateTimeObj = pattern.parseDateTime("2019.09.17 AD at 15:29:00 IST");
          System.out.println(dateCtxParamDateTimeObj.toDate());
      }
  </code></pre>
  
  <p><strong>Output</strong></p>
  
  <pre><code>Tue Sep 17 15:29:00 IST 2019
  Exception in thread "main" java.lang.IllegalArgumentException: Invalid format: "2019.09.17 AD at 15:29:00 IST" is malformed at "IST"
      at org.joda.time.format.DateTimeFormatter.parseDateTime(DateTimeFormatter.java:945)
  </code></pre>