[action] [PR:27669] [vm_set]: Enable ptf_use_docker_network for BMC topology only when the docker network exists

[mssonicbld]

Description of PR

Summary:
Fixes #26542

#26405 sets ptf_use_docker_network to true for every BMC topology. In that mode the PTF container is created with network_mode: {{ mgmt_bridge }} plus a static IP on a docker network of that name, and the Bind topology step that would otherwise give the PTF a veth on the Linux management bridge is skipped. On servers whose mgmt_bridge is a Linux bridge there is no docker network of that name, so add-topo fails at Create ptf container with Parameter error: network named br0 could not be found.

This change probes for the docker network with docker network inspect {{ mgmt_bridge }} and enables the mode only when the network exists. Servers that have it keep the docker network path introduced by #23813 and #26405. Servers without it keep the Linux-bridge path, where the bind step attaches a veth into the PTF netns. An explicit ptf_use_docker_network setting from group_vars or host_vars still wins, since both new tasks skip when the variable is already defined.

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• New Test case
  • Skipped for non-supported platforms
• Test case improvement

Back port request

• 202311
• 202405
• 202411
• 202505
• 202511
• 202512
• 202605

Tracking issue/work item for backport/cherry-pick request (GitHub issue or Microsoft ADO): #26542
Failure type: regression

Tested branch

• master

Test result

• master: bmc-shared-mgmt topology on a test server where mgmt_bridge is a Linux bridge and no docker network of that name exists. Before the change, add-topo fails at Create ptf container as reported in #26542. With the change, Check whether a docker network named "br0" exists returns rc 1, the enable task is skipped, Create ptf container and Bind topology bmc-shared-mgmt to VMs both report changed, and the play ends with failed=0.

Approach

What is the motivation for this PR?

Restore add-topo for BMC topologies on servers that use a Linux management bridge, which #26405 broke by assuming a docker network named after mgmt_bridge is present.

How did you do it?

In add_topo.yml and renumber_topo.yml, replace the unconditional set_fact: ptf_use_docker_network: true for BMC topologies with a docker network inspect {{ mgmt_bridge }} probe (failed_when: false, changed_when: false) followed by the same set_fact, now conditioned on the probe returning rc 0. Both tasks run only when 'bmc' in topo and ptf_use_docker_network is not already defined.

How did you verify/test it?

See Test result. The probe-positive branch (docker network present, docker mode enabled) is the same code path #26405 exercised.

Any platform specific information?

Applies to BMC topologies only. No change for other topologies.

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

N/A

Documentation

N/A

Signed-off-by: Sonic Build Admin sonicbld@microsoft.com

[mssonicbld]

Original PR: sonic-net/sonic-mgmt#27669

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