[sonic-config-engine] Replace os.system, replace yaml.load, remove subprocess with shell=True

[maipbui]

Signed-off-by: maipbui [email protected]

Why I did it

Missing import statement in PR https://github.com/sonic-net/sonic-buildimage/pull/12533

How I did it

Revert PR 12646 Add import statement

1. https://github.com/sonic-net/sonic-buildimage/blob/31f7afa92e8d1e353ef2f3b004711dd18c0d94f6/src/sonic-config-engine/tests/test_j2files_t2_chassis_fe.py#L8
2. https://github.com/sonic-net/sonic-buildimage/blob/31f7afa92e8d1e353ef2f3b004711dd18c0d94f6/src/sonic-config-engine/tests/test_j2files.py#L8
3. https://github.com/sonic-net/sonic-buildimage/blob/31f7afa92e8d1e353ef2f3b004711dd18c0d94f6/src/sonic-config-engine/tests/test_multinpu_cfggen.py#L11

How to verify it

Pass UT

Which release branch to backport (provide reason below if selected)

• [ ] 201811
• [ ] 201911
• [ ] 202006
• [ ] 202012
• [ ] 202106
• [ ] 202111
• [ ] 202205

Description for the changelog

Ensure to add label/tag for the feature raised. example - PR#2174 under sonic-utilities repo. where, Generic Config and Update feature has been labelled as GCU.

Link to config_db schema for YANG module changes

A picture of a cute animal (not mandatory but encouraged)

[qiluo-msft]

This PR looks good to me. Could you dig deeper why the reverted PR was not caught by testcases on Github repo? Do we have test gap?