[console] Add console baud rate test

[yaqiangz]

Description of PR

Summary:
Fixes # 5399

Type of change

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

Back port request

• 201911
• 202012
• 202205

Approach

What is the motivation for this PR?

Add test case to verify the console's baud rate is 9600

How did you do it?

1. Verify console baud rate in sonic by cmdfile.
2. Connect to DUT by console to verify the actual baud rate.
3. While connecting by console, reboot to aboot/onie to verify baud rate.

How did you verify/test it?

Run tests

collected 3 items

dut_console/test_console_baud_rate.py::test_console_baud_rate_config PASSED                                                                                                                  [ 33%]
dut_console/test_console_baud_rate.py::test_baud_rate_sonic_connect PASSED                                                                                                                   [ 66%]
dut_console/test_console_baud_rate.py::test_baud_rate_boot_connect PASSED                                                                                                                    [100%]

Any platform specific information?

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

Documentation

[yaqiangz]

@Blueve Could you pls help to review this PR?

[yaqiangz]

/azp run

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[yaqiangz]

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[yaqiangz]

/azp run

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