[BUG] Failed zombie handling test also fails the subsequent sig term handling test

[sysarch-repo]

Describe the bug
If the zombie handling tests fails when running cert / cert essential tests then the sig term handling test fails as well.

To Reproduce
Steps to reproduce the behavior:

1. Install testsuite 1.3.3
2. Deploy AUT that does not handle zombie reaping but does handle sig term
3. Run cert or cert essential tests
4. See zombie handling test and also sig term handling test failing
5. Run the sig term handling test in isolation and note it will pass

Assumptions:
From the sig term handling log:

I, [2025-01-01 22:31:17 UTC #11785]  INFO -- cnf-testsuite: KubectlClient.exec command: kubectl exec -n cnf-testsuite -ti cluster-tools-dkvzh -- bash -c 'sleep 10 && kill 33069 && sleep 5 && kill -9 33069’
bash: line 1: kill: (33069) - No such process
command terminated with exit code 1

Either the process terminates immediately and so there is no process to kill after 5 seconds, or the sig term handling test is confused by orphaned zombie processes left behind from the failed zombie handling test, e.g.:

  PID  PPID USER     STAT   VSZ %VSZ CPU %CPU COMMAND
    1     0 1000     S    1207m   4%   1   0% /usr/local/bin/app1
   28     0 1000     S     1672   0%   6   0% sh
   49    28 1000     R     1600   0%  10   0% top
   47     1 1000     Z        0   0%  14   0% [sleep] <- zombie
   46     1 1000     Z        0   0%   9   0% [sleep] <- zombie

Expected behavior
Failed zombie handling test shall have no impacts on the result of the subsequent sig term handling test.

[svteb]

Will look into this as part of #2197 .