fix host out readlines

Author: peterstone2017

azure_functions_worker/testutils.py

@@ -899,7 +899,11 @@ def start_webhost(*, script_dir=None, stdout=None):
 
     addr = f'http://{LOCALHOST}:{port}'
     health_check_endpoint = f'{addr}/api/ping'
-    host_out = stdout.readlines(100)
+    host_out = ""
+    if stdout is not None and hasattr(stdout,
+                                      "readable") and stdout.readable():
+        host_out = stdout.readlines(100)
+
     for _ in range(5):
         try:
             r = requests.get(health_check_endpoint,