Fix custom metrics test

It gives this error when running:
```
Output of kubectl metrics:
{"accountidentity": "", "subresources": "-", "pods": "0", "containers": "0", "nodes": "0", "cpu": "0.0 m", "memory": "0.0 Mi", "storage": "0 Gi", "networkReceiveBytes": "0 bytes", "networkTransmitBytes": "0 bytes", "notRunningPods": "0", "oom_events": "0"}

FAIL: The custom field 'hello_requests_total' does not exist in the metrics JSON output.
E
======================================================================
ERROR: test_metrics_custom (__main__.TestKubePlus.test_metrics_custom)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/ishan/go/src/github.com/cloud-ark/kubeplus/tests/tests.py", line 766, in test_metrics_custom
sys.exit(1)
SystemExit: 1

----------------------------------------------------------------------
Ran 1 test in 19.520s

FAILED (errors=1)
```

Start with tests/tests.py and the test_metrics_custom function, then run the failing test and inspect the kubectl metrics output shown in the issue. Trace why hello_requests_total is absent from the returned metrics JSON; done means the custom metrics test passes and the expected field is present.

Written by the indexing model from the issue text.