fix case when nmcli is present but does not handle dns

tests/test_dns_records.py

@@ -17,13 +17,16 @@ from envsetup import utils as u  # noqa: E402
 
 
 def get_dns_servers() -> set:
+    servers = list()
+
     if subprocess.getstatusoutput("command -v nmcli")[0] == 0:
         # network-manager
         _, output = subprocess.getstatusoutput(
             "nmcli -f all device show | grep IP4.DNS | awk '{ print $2 }'"
         )
         servers = output.split("\n")
-    else:
+
+    if not len(servers):
         # resolvconf
         with open("/etc/resolv.conf", "r") as f:
             d = f.read().strip()