dns-provider=kube-dns fails in K8s 1.20

Hi team,

test_dns_provider never stops on K8s 1.20 as the charm fails to enable kube-dns and the test waits for coredns pod to be removed:

============================= test session starts ==============================
platform linux -- Python 3.8.5, pytest-6.0.2, py-1.9.0, pluggy-0.13.1 -- /home/ubuntu/k8s-validation/.tox/py3/bin/python
cachedir: .tox/py3/.pytest_cache
metadata: {'Python': '3.8.5', 'Platform': 'Linux-5.4.0-51-generic-x86_64-with-glibc2.29', 'Packages': {'pytest': '6.0.2', 'py': '1.9.0', 'pluggy': '0.13.1'}, 'Plugins': {'flaky': '3.7.0', 'metadata': '1.10.0', 'asyncio': '0.14.0', 'html': '2.1.1'}}
rootdir: /home/ubuntu/k8s-validation, configfile: pytest.ini
plugins: flaky-3.7.0, metadata-1.10.0, asyncio-0.14.0, html-2.1.1
collecting ... collected 1 item

jobs/integration/validation.py::test_dns_provider
-------------------------------- live log setup --------------------------------
unknown facade CAASModelOperator
unexpected facade CAASModelOperator found, unable to decipher version to use
unknown delta type: id
Waiting for coredns pods to be removed

2021-03-25-18:42:17 root ERROR [localhost] STDERR follows:
None
Traceback (most recent call last):
  File "/usr/local/bin/fce", line 11, in <module>
    load_entry_point('foundationcloudengine', 'console_scripts', 'fce')()
  File "/home/ubuntu/deployment/cpe-foundation/foundationcloudengine/foundationcloudengine/main.py", line 168, in entry_point
    sys.exit(main(sys.argv[1:]))
  File "/home/ubuntu/deployment/cpe-foundation/foundationcloudengine/foundationcloudengine/main.py", line 159, in main
    opts.func(opts)
  File "/home/ubuntu/deployment/cpe-foundation/foundationcloudengine/foundationcloudengine/validate.py", line 41, in validate_main
    layer.validate(tests=args.validators)
  File "/home/ubuntu/deployment/cpe-foundation/foundationcloudengine/foundationcloudengine/layers/baselayer.py", line 200, in validate
    validator.run()
  File "/home/ubuntu/deployment/cpe-foundation/foundationcloudengine/foundationcloudengine/layers/baselayer.py", line 430, in run
    self.run_inner()
  File "/home/ubuntu/deployment/cpe-foundation/foundationcloudengine/foundationcloudengine/layers/kubernetes.py", line 205, in run_inner
    self.run_tests(controller, model)
  File "/home/ubuntu/deployment/cpe-foundation/foundationcloudengine/foundationcloudengine/layers/kubernetes.py", line 234, in run_tests
    local(cmd, output_mode="live", env=my_env)
  File "/home/ubuntu/deployment/cpe-foundation/foundationcloudengine/foundationcloudengine/remotehelpers.py", line 209, in local
    return run_cmd(cmd, target_machine, **kwargs)
  File "/home/ubuntu/deployment/cpe-foundation/foundationcloudengine/foundationcloudengine/remotehelpers.py", line 147, in run_cmd
    raise subprocess.CalledProcessError(ps.returncode, cmd, output=out, stderr=err)

Looking in the kubernetes-master's Juju logs we see this:

2021-03-25 19:29:39 INFO juju-log Invoking reactive handler: reactive/kubernetes_master.py:1424:configure_cdk_addons
2021-03-25 19:30:03 WARNING update-status Resource: "/v1, Resource=services", GroupVersionKind: "/v1, Kind=Service"
2021-03-25 19:30:45 WARNING update-status Name: "kube-dns", Namespace: "kube-system"
2021-03-25 19:30:49 INFO juju-log Checking if snap.kube-apiserver.daemon is active (0 / 6)
2021-03-25 19:34:52 WARNING update-status
2021-03-25 19:35:35 WARNING update-status cmd ['/snap/cdk-addons/5273/kubectl', '--kubeconfig', '/root/cdk/cdk_addons_kubectl_config', 'apply', '-f', '/root/snap/cdk-addons/5273/addons/kube2021-03-25 19:35:56 WARNING update-status Resource: "/v1, Resource=services", GroupVersionKind: "/v1, Kind=Service"
2021-03-25 19:35:56 WARNING update-status Name: "kube-dns", Namespace: "kube-system"
2021-03-25 19:35:56 WARNING update-status for: "/root/snap/cdk-addons/5273/addons/kube-dns.yaml": Service "kube-dns" is invalid: spec.clusterIPs[0]: Invalid value: "dns_server": must be a valid IP address, (e.g. 10.9.8.7 or 2001:db8::ffff)
2021-03-25 19:35:56 WARNING update-status Error from server (BadRequest): error when creating "/root/snap/cdk-addons/5273/addons/kube-dns.yaml": Deployment in version "v1" cannot be handled as a Deployment: v1.Deployment.Spec: v1.DeploymentSpec.Template: v1.PodTemplateSpec.Spec: v1.PodSpec.Containers: []v1.Container: v1.Container.Resources: v1.ResourceRequirements.Requests: Limits: unmarshalerDecoder: quantities must match the regular expression '^([+-]?[0-9.]+)([eEinumkKMGTP]*[-+]?[0-9]*)$', error found in #10 byte of ...|ory_limit"},"request|..., bigger context ...|"resources":{"limits":{"memory":"dns_memory_limit"},"requests":{"cpu":"100m","memory":"70Mi"}},"secu|...
2021-03-25 19:35:56 INFO juju-log Addons are not ready yet.

Please fix.