test_lldp_syncd.py: Provide enough ready time for flap, restart, and reboot testcases

[honllum]

Description of PR

Provide enough ready time for flap, restart, and reboot testcases.

For flap testcase, sometimes get_lldp_entry_content() will return empty entry content even though the testcase has just verified the entry content using the same function. It seems we need to provide enough time for the DB object to be ready again for query. Also increase wait_until() timeout from 60 seconds to 120 seconds.

For restart testcase, increase wait_until() timeout from 60 seconds to 120 seconds.

For reboot testcase, DB takes more time to be ready after DUT/LLDP is up, thus adding a verify DB keys assertion check after DUT rebooted before proceeding to the rest of the assertion checks.

Summary:
Fixes # (issue)

Type of change

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

Back port request

• 202012
• 202205
• 202305
• 202311
• 202405

Approach

What is the motivation for this PR?

Fixing testcode.

How did you do it?

Explained above.

How did you verify/test it?

Tested on HW topo.

Any platform specific information?

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

Documentation

[mssonicbld]

The pre-commit check detected issues in the files touched by this pull request.
The pre-commit check is a mandatory check, please fix detected issues.

Detailed pre-commit check results:
trim trailing whitespace.................................................Failed
- hook id: trailing-whitespace
- exit code: 1
- files were modified by this hook

Fixing tests/lldp/test_lldp_syncd.py

fix end of files.........................................................Passed
check yaml...........................................(no files to check)Skipped
check for added large files..............................................Passed
check python ast.........................................................Passed
flake8...................................................................Failed
- hook id: flake8
- exit code: 1

tests/lldp/test_lldp_syncd.py:149:1: E302 expected 2 blank lines, found 1
tests/lldp/test_lldp_syncd.py:156:1: E302 expected 2 blank lines, found 1
tests/lldp/test_lldp_syncd.py:223:9: F821 undefined name 'time'
tests/lldp/test_lldp_syncd.py:223:22: E261 at least two spaces before inline comment
...
[truncated extra lines, please run pre-commit locally to view full check results]

To run the pre-commit checks locally, you can follow below steps:

1. Ensure that default python is python3. In sonic-mgmt docker container, default python is python2. You can run
   the check by activating the python3 virtual environment in sonic-mgmt docker container or outside of sonic-mgmt
   docker container.
2. Ensure that the pre-commit package is installed:

sudo pip install pre-commit

3. Go to repository root folder
4. Install the pre-commit hooks:

pre-commit install

5. Use pre-commit to check staged file:

pre-commit

6. Alternatively, you can check committed files using:

pre-commit run --from-ref <commit_id> --to-ref <commit_id>

[mssonicbld]

The pre-commit check detected issues in the files touched by this pull request.
The pre-commit check is a mandatory check, please fix detected issues.

Detailed pre-commit check results:
trim trailing whitespace.................................................Failed
- hook id: trailing-whitespace
- exit code: 1
- files were modified by this hook

Fixing tests/lldp/test_lldp_syncd.py

fix end of files.........................................................Passed
check yaml...........................................(no files to check)Skipped
check for added large files..............................................Passed
check python ast.........................................................Passed
flake8...................................................................Failed
- hook id: flake8
- exit code: 1

tests/lldp/test_lldp_syncd.py:149:1: E302 expected 2 blank lines, found 1
tests/lldp/test_lldp_syncd.py:156:1: E302 expected 2 blank lines, found 1
tests/lldp/test_lldp_syncd.py:223:22: E261 at least two spaces before inline comment

flake8...............................................(no files to check)Skipped
...
[truncated extra lines, please run pre-commit locally to view full check results]

To run the pre-commit checks locally, you can follow below steps:

1. Ensure that default python is python3. In sonic-mgmt docker container, default python is python2. You can run
   the check by activating the python3 virtual environment in sonic-mgmt docker container or outside of sonic-mgmt
   docker container.
2. Ensure that the pre-commit package is installed:

sudo pip install pre-commit

3. Go to repository root folder
4. Install the pre-commit hooks:

pre-commit install

5. Use pre-commit to check staged file:

pre-commit

6. Alternatively, you can check committed files using:

pre-commit run --from-ref <commit_id> --to-ref <commit_id>

[honllum]

Issue fixed by #15331 , #15337. Closing this PR.