[tests/generic_config_updater] implement AAA test for generic config …

…updater(#4915)

Summary: 
Testcase of AAA for generic updater apply-patch

What is the motivation for this PR?
End to End test support for Generic Updater apply-patch
This PR is to verify the usage of 'config apply-patch' works on AAA

How did you do it?
Make some config apply change. And check if the AAA config changed as expected.

How did you verify/test it?
Run test of sonic-mgmt/tests/generic_config_updater/test_aaa.py on KVM