[action] [PR:18666] [dualtor] Fix test_orchagent_slb

[mssonicbld]

Description of PR

Summary:
Fixes # (issue)

Type of change

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

Back port request

• 202205
• 202305
• 202311
• 202405
• 202411
• 202505

Approach

What is the motivation for this PR?

Fix test_orchagent_slb:

1. the exabgp log collection log has an issue that the logs might not exists before test, so it will error in this case.
2. when the slb sessions withdraw the route, the upper ToR slb session withdraws first, then the lower ToR; so there is a time period that, the route is withdrawed from the upper ToR but not the lower ToR, T1s still have this route learnt from the lower ToR so that the upper ToR have this route in its FIB that is learnt from T1s and has nexthops as T1s.
   So, let's wait for more time to allow the lower ToR withdraw to happen.

How did you do it?

1. ignore exabgp log not exist error in log collection.
2. add wait_until logic for the withdraw check.

How did you verify/test it?

dualtor/test_orchagent_slb.py::test_orchagent_slb[ipv4-active-standby] PASSED [100%]

============================================================================================================================== warnings summary ==============================================================================================================================
../../../../../usr/local/lib/python3.8/dist-packages/paramiko/transport.py:236
 /usr/local/lib/python3.8/dist-packages/paramiko/transport.py:236: CryptographyDeprecationWarning: Blowfish has been deprecated
 "class": algorithms.Blowfish,

dualtor/test_orchagent_slb.py: 96 warnings
 /usr/local/lib/python3.8/dist-packages/ptf/mask.py:69: DeprecationWarning: "set_do_not_care_scapy" is going to be deprecated, please switch to the new one: "set_do_not_care_packet"
 warnings.warn(

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
========================================================================================================== 1 passed, 3 deselected, 97 warnings in 554.61s (0:09:14) ==========================================================================================================

Any platform specific information?

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

Documentation

[mssonicbld]

Original PR: #18666

[mssonicbld]

/azp run

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