final_message: allow replacement of capital name keys.

documentation of final_message in 
  doc/examples/cloud-config-final-message.txt
showed '$UPTIME' and '$TIMESTAMP' would be available, but
only the lower case versions of these strings were available.

This change just makes all lower case and upper case keys
available here to avoid breaking anyone who used the
functional-but-not-correctly-documented lower case names.

cloudinit/config/cc_final_message.py

@@ -53,6 +53,7 @@ def handle(_name, cfg, cloud, log, args):
             'version': cver,
             'datasource': str(cloud.datasource),
         }
+        subs.update(dict([(k.upper(), v) for k, v in subs.items()]))
         util.multi_log("%s\n" % (templater.render_string(msg_in, subs)),
                        console=False, stderr=True, log=log)
     except Exception: