Use display.display for executor debug messages

These debug messages are not useful in the log file - but they showing
them on stdout in tests could be more useful.

Change-Id: I5c07c389fe72b440d8f9da1dab5354b34c5dcdec
diff --git a/zuul/ansible/callback/zuul_stream.py b/zuul/ansible/callback/zuul_stream.py
index 4424bb9..ed0306b 100644
--- a/zuul/ansible/callback/zuul_stream.py
+++ b/zuul/ansible/callback/zuul_stream.py
@@ -103,14 +103,14 @@
         self._log = logging.getLogger('zuul.executor.ansible')
 
     def _read_log(self, host, ip, log_id, task_name):
-        self._log.debug("[%s] Starting to log %s for task %s"
-                        % (host, log_id, task_name))
+        self._display.display("[%s] Starting to log %s for task %s"
+                              % (host, log_id, task_name))
         s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
         while True:
             try:
                 s.connect((ip, LOG_STREAM_PORT))
             except Exception:
-                self._log.debug("[%s] Waiting on logger" % host)
+                self._display.vvv("[%s] Waiting on logger" % host)
                 time.sleep(0.1)
                 continue
             msg = "%s\n" % log_id
@@ -173,6 +173,7 @@
                 msg = "{now} | [Zuul] Log Stream did not terminate".format(
                     now=datetime.datetime.now())
                 self._log.info(msg)
+                self._display.display("WARNING: Streamer could not join")
 
     def v2_runner_on_failed(self, result, ignore_errors=False):
         self._stop_streamer()