Remove any null characters before parsing string in test_snmp_phy_entity

[Janetxxx]

Description of PR

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?

Solve ValueError when parsing a string that contains null bytes (\x00). ast.literal_eval is essentially trying to compile a string into an Abstract Syntax Tree node, but it can't handle null bytes in the string. e,g., node_or_string = '{\'ext_identifier\': \'Power Class 8 (16.0W Max)\', \'media_lane_count\': \'N/A\', \'ma: \'2024-05-23 \x00\x00\', \'active_apsel_hostlane7\': \'N/A\'}'

This happens due to how the output is captured by the shell command execution cmd = 'sonic-db-cli {} HGETALL \"{}\"'.format(db_id, key) output = duthost.shell(cmd)The output is being captured as a string with escaped single quotes and some null characters.

How did you do it?

Remove any null characters before parsing string.

How did you verify/test it?

In snmp/test_snmp_phy_entity.py:

======================================================================================== short test summary info ========================================================================================

SKIPPED [1] snmp/test_snmp_phy_entity.py:367: Not supported on non supervisor node

SKIPPED [1] platform_tests/thermal_control_test_helper.py:123: No mocker defined for this platform x86_64-arista_7060x6_64pe

SKIPPED [1] snmp/test_snmp_phy_entity.py:636: psu_controller is None, skipping this test

========================================================================== 4 passed, 3 skipped, 1 warning in 853.68s (0:14:13) ==========================================================================

Any platform specific information?

str3-7060x6-64pe-1

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

t0-standalone-32

Documentation