[Copp]Refactor coppmgr mock tests

[dgsudharsan]

What I did
Refactoring coppmgr mock tests

Why I did it
After migration to bookworm, coppmgr tests started failing due to the use of sudo commands.

[----------] 1 test from CoppMgrTest
[ RUN      ] CoppMgrTest.CoppTest
sudo: pam_open_session: Too many open files
sudo: policy plugin failed session initialization
copp_ut.cpp:28: Failure
Expected equality of these values:
 status
Which is: 256
 0
CoppMgrTest.CoppTest (107 ms)
1 test from CoppMgrTest (107 ms total)

Avoided the logic of replacing the files using sudo by slightly refactoring the code.
How I verified it
Run the UT to verify.

Details if related