[centos7] Test{,Systemd}Freeze FAIL: unexpected error: unable to freeze

Hmm, we are getting this a lot lately :-\

Last example is from https://github.com/opencontainers/runc/pull/2868/checks?check_run_id=2299195550

```
=== RUN   TestSystemdFreeze
    utils_test.go:86: exec_test.go:539: unexpected error: unable to freeze
        
--- FAIL: TestSystemdFreeze (1.17s)
```