For some reason, microshift-test-agent.sh gets terminated twice very quickly which doesn't let `chattr -i` clean up the backups dir immutability.

17/257 =~ 6.6%

1. Deploy R4E system
2. Edit the microshift-test-agent.sh to not check the boot_counter (so it's active always, not only on staged deployments)
3. Set up /var/lib/microshift-test-agent.json so that the currently active deployment gets `prevent_backup` action, e.g.:
{"rhel-df05aafa1c86eeb1f91293ec4adabcd6c10f52f2526c4bb8d82b1d7d735b54e5.0": { "every": ["prevent_backup"]}}
4. In a loop:
   a. Reboot the host
   b. Grep microshift-test-agent's journal for line that confirms successful removal of immutability:

ssh HOST "sudo journalctl -u microshift-test-agent -b-1 --grep 'Flags of /var/lib/microshift-backups set as ---------'"

microshift-test-agent.sh[754]: Terminated
microshift-test-agent.sh[754]: ++ _cleanup
microshift-test-agent.sh[754]: ++ for cmd in "${CLEANUP_CMDS[@]}" 
microshift-test-agent.sh[754]: ++ chattr -V -i /var/lib/microshift-backups
microshift-test-agent.sh[754]: Terminated
systemd[1]: microshift-test-agent.service: Main process exited, code=exited, status=143/n/a
systemd[1]: microshift-test-agent.service: Failed with result 'exit-code'.

microshift-test-agent exits successfully, its journal contains

> Flags of /var/lib/microshift-backups set as ---------