[action] [PR:12890] Fix sonic-mgmt testbed-cli interface_to_vms undefined failure.

[mssonicbld]

Description of PR

Summary:
If any topology without any VMs, e.g. no T1s for T0 topology, the testbed-cli deploy-mg will fail, due to error below:

TASK [find all interface names] *****************************************************************************************************************************************************************************
task path: /var/src/mgmt-int/ansible/config_sonic_basedon_testbed.yml:273
Sunday 19 May 2024 18:06:26 +0000 (0:00:00.021) 0:00:16.756 ************
fatal: [str3-7060x6-64pe-1]: FAILED! => {
 "msg": "'interface_to_vms' is undefined"
}

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• Test case(new/improvement)

Back port request

• 201911
• 202012
• 202205
• 202305
• 202311

Approach

What is the motivation for this PR?

This change is to fix the error above, when VM list is empty.

How did you do it?

The fix is straightforward - to give it a default value that is an empty list when enumerating.

How did you verify/test it?

The change is run locally with topology with empty VMs, and it works.

Any platform specific information?

No.

Supported testbed topology if it's a new test case?

Documentation

No doc needs to be updated for this change.

[mssonicbld]

/azp run

[mssonicbld]

Original PR: #12890

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