fix empty string NSG's DestinationAddressPrefix

[kon-angelo]

What type of PR is this?

What this PR does / why we need it:

On special (aka undetermined) cases, the Azure API may return an empty string for security group's DestinationAddressPrefixes. For example:

 ...
       "destinationAddressPrefix": "",
        "destinationAddressPrefixes": [
          "20.23.46.159"
        ],
...
        "destinationAddressPrefix": "",
        "destinationAddressPrefixes": [
          "20.31.182.144",
          "20.103.204.84",
          "20.93.254.98",
...

As a result, the request to update the NSG may contain incorrect DAP prefixes resulting to an error like the following:

{
     "name": "k8s-azure-lb_allow_IPv4_a4dbc5c93f3bdd7a058a3939da862f9c",
     "properties": {
      "access": "Allow",
      "destinationAddressPrefixes": [
       "", <--------------- not supported -------------
       "20.101.205.120",
       "20.101.205.84",
       "20.103.202.213",
      ],
      "destinationPortRange": "",
      "destinationPortRanges": [
       "15021",
       "443",
       "80"
      ],
      "direction": "Inbound",
      "priority": 545,
      "protocol": "Tcp",
      "sourceAddressPrefix": "Internet",
      "sourceAddressPrefixes": [],
      "sourcePortRange": "*",
      "sourcePortRanges": []
     },
     "type": "Microsoft.Network/networkSecurityGroups/securityRules"
    }
}

With this PR, we will skip including the empty string with the NSG patch requests.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Fix a bug that prevented patches to NSGs when the Azure API responded with empty strings for `DestinationAddressPrefix`

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @kon-angelo. Thanks for your PR.

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[andyzhangx]

/ok-to-test

[andyzhangx]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andyzhangx, kon-angelo

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[k8s-ci-robot]

@kon-angelo: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-cloud-provider-azure-e2e-ccm-vmss-ip-lb-capz	ca1959b	link	true	/test pull-cloud-provider-azure-e2e-ccm-vmss-ip-lb-capz
pull-cloud-provider-azure-e2e-ccm-vmss-capz	ca1959b	link	true	/test pull-cloud-provider-azure-e2e-ccm-vmss-capz

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.