[tests] deal with the No Such Record lines in the output of dns-sd (

#11223)

When resolving a hostname, `dns-sd` may output a line saying `No Such
Record` with an all-zero address which should be discarded.

tests/scripts/thread-cert/node.py

@@ -4040,6 +4040,8 @@ def discover_mdns_service(self, instance, name, host_name, timeout=2):
         for line in self.bash(f'cat {host_name_file}', encoding='raw_unicode_escape'):
             elements = line.split()
             fullname = f'{host_name}.local.'
+            if 'No Such Record' in line:
+                continue
             if fullname not in elements:
                 continue
             if 'Add' not in elements: