Fix Python error in check_tirex

Author: Nakaner

ansible/roles/tileserver_step2/files/monitoring/tirex/check_tirex.py

@@ -22,7 +22,7 @@ class ServiceStatus(Enum):
     UNKNOWN = 3
 
 
-def respond(status, message, measurements):
+def respond(status, message, measurements=None):
     if not measurements:
         line = "{}: {}\n".format(status.name, message)
     else: